[Flight & DevTools] Strip the whole "async " prefix from V8 stack frame names (react#37608)

## Summary

V8 prefixes async call sites with `async ` when it prints a stack, like
this:

```
Error: boom
    at inner (/tmp/asy.js:1:44)
    at async outerName (/tmp/asy.js:2:30)
```

`parseStackTraceFromChromeStack` captures `async outerName` as the frame
name and strips the prefix here:

```js
} else if (name.startsWith('async ')) {
  name = name.slice(5);
  isAsync = true;
}
```

`'async '` is six characters, so `slice(5)` leaves the space behind and
the frame name comes back as `' outerName'` rather than `'outerName'`.

I noticed it while reading the parser, and it is not purely cosmetic:
that name is the first element of the `ReactFunctionLocation` returned
by `extractLocationFromComponentStack` and
`extractLocationFromOwnerStack`, which `backend/fiber/renderer.js`
stores as `instance.source`. Any async component whose frame reaches
that path is recorded under a name with a stray leading space.

The same line exists in
`packages/react-server/src/ReactFlightStackConfigV8.js`, which the
DevTools file is a copy of. After review I fixed it in this PR as well,
in a second commit. There it only matters on the fallback path that
parses an already formatted stack string, when the error's `stack` was
read or assigned before React reaches it. react#37130 is open on that file
too, but it does not touch these lines.

## How did you test this change?

I first confirmed the format V8 actually emits, rather than assuming it:

```
$ node -e 'async function inner(){await null;throw new Error("boom")}
async function outerName(){await inner()}
outerName().catch(e=>console.log(e.stack))'
Error: boom
    at inner ([eval]:1:52)
    at async outerName ([eval]:2:33)
```

Then I added a case to the existing `extractLocationFromComponentStack`
block in `utils-test.js`. Against `main` it fails with exactly the
leading space:

```
  ● utils › extractLocationFromComponentStack › should strip the async prefix from a frame name

    - Expected  - 1
    + Received  + 1

      Array [
    -   "Comments",
    +   " Comments",
        "https://react.dev/_next/static/chunks/848-122f91e9565d9ffa.js",
        5,
        9236,
      ]
```

With the one-character fix applied:

```
$ yarn test --build --project=devtools -r=experimental utils-test
PASS packages/react-devtools-shared/src/__tests__/utils-test.js
Tests:       63 passed, 63 total
```

I also ran the whole DevTools project before and after to check I was
not moving anything else. Both runs end at `9 failed, 4 failed suites`,
the same test names each time (`componentStacks`, `console`,
`inspectedElement`, `legacy/inspectElement`), so those failures are
pre-existing on `main` in my environment and unrelated to this change.
The only difference between the two runs is my new test: 586 passed
before, 587 after.

For the Flight side I added `ReactFlightStackConfigV8-test.js`, which
assigns a formatted stack to an error and checks what `parseStackTrace`
returns. Against `main` it fails with the same leading space (`"
outerName"`); with the fix it passes on stable and experimental in
development. It is gated to `__DEV__` because that fallback goes through
the DEV-only stack cache. `ReactFlightServer-test` and
`ReactFlightAsyncDebugInfo-test` still pass next to it (23 tests).

`prettier` and `eslint` are clean on all changed files. `yarn flow
dom-node` reported no errors for the DevTools commit; I did not rerun
Flow after the one-character Flight change.

AI tools used

Author: Dev-next-gen

packages/react-devtools-shared/src/__tests__/utils-test.js

@@ -395,6 +395,19 @@ describe('utils', () => {
       ]);
     });
 
+    it('should strip the async prefix from a frame name', () => {
+      expect(
+        extractLocationFromComponentStack(
+          '    at async Comments (https://react.dev/_next/static/chunks/848-122f91e9565d9ffa.js:5:9236)',
+        ),
+      ).toEqual([
+        'Comments',
+        'https://react.dev/_next/static/chunks/848-122f91e9565d9ffa.js',
+        5,
+        9236,
+      ]);
+    });
+
     it('should support Firefox stack', () => {
       expect(
         extractLocationFromComponentStack(

packages/react-devtools-shared/src/backend/utils/parseStackTrace.js

@@ -45,7 +45,7 @@ function parseStackTraceFromChromeStack(
     if (name === '<anonymous>') {
       name = '';
     } else if (name.startsWith('async ')) {
-      name = name.slice(5);
+      name = name.slice(6);
       isAsync = true;
     }
     let filename = parsed[2] || parsed[5] || '';

packages/react-server/src/ReactFlightStackConfigV8.js

@@ -237,7 +237,7 @@ export function parseStackTrace(
     if (name === '<anonymous>') {
       name = '';
     } else if (name.startsWith('async ')) {
-      name = name.slice(5);
+      name = name.slice(6);
       isAsync = true;
     }
     let filename = parsed[2] || parsed[5] || '';

packages/react-server/src/__tests__/ReactFlightStackConfigV8-test.js

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ * @jest-environment node
+ */
+
+'use strict';
+
+let parseStackTrace;
+
+describe('ReactFlightStackConfigV8', () => {
+  beforeEach(() => {
+    jest.resetModules();
+    parseStackTrace =
+      require('react-server/src/ReactFlightStackConfigV8').parseStackTrace;
+  });
+
+  // @gate __DEV__
+  it('strips the async prefix from a frame name in an already formatted stack', () => {
+    const error = new Error();
+    // Assigning the stack means V8 never calls prepareStackTrace, so the
+    // parser has to fall back to reading the formatted string.
+    error.stack =
+      'Error: boom\n' +
+      '    at inner (/tmp/app.js:1:44)\n' +
+      '    at async outerName (/tmp/app.js:2:30)';
+
+    expect(parseStackTrace(error, 1)).toEqual([
+      ['inner', '/tmp/app.js', 1, 44, 0, 0, false],
+      ['outerName', '/tmp/app.js', 2, 30, 0, 0, true],
+    ]);
+  });
+});