Generalize Segment Cache fallback implementation (#84652)

This is a stack of refactors related to the internal map type used to
store Segment Cache entries on the client. Refer to each commit message
for full details.

The main motivation is to generalize the "fallback entry" mechanism used
for interception routes to more kinds of params. Currently this is only
used for interception routes and search params, but in the future we
will use it for route params, too.

Author: acdlite

packages/next/src/client/components/segment-cache-impl/cache-key.ts

@@ -2,14 +2,14 @@
 type Opaque<K, T> = T & { __brand: K }
 
 // Only functions in this module should be allowed to create CacheKeys.
-export type NormalizedHref = Opaque<'NormalizedHref', string>
+export type NormalizedPathname = Opaque<'NormalizedPathname', string>
 export type NormalizedSearch = Opaque<'NormalizedSearch', string>
 export type NormalizedNextUrl = Opaque<'NormalizedNextUrl', string>
 
 export type RouteCacheKey = Opaque<
   'RouteCacheKey',
   {
-    href: NormalizedHref
+    pathname: NormalizedPathname
     search: NormalizedSearch
     nextUrl: NormalizedNextUrl | null
 
@@ -21,11 +21,9 @@ export function createCacheKey(
   originalHref: string,
   nextUrl: string | null
 ): RouteCacheKey {
-  // TODO: We should remove the hash from the href and track that separately.
-  // There's no reason to vary route entries by hash.
   const originalUrl = new URL(originalHref)
   const cacheKey = {
-    href: originalHref as NormalizedHref,
+    pathname: originalUrl.pathname as NormalizedPathname,
     search: originalUrl.search as NormalizedSearch,
     nextUrl: nextUrl as NormalizedNextUrl | null,
   } as RouteCacheKey