perf(keyring-controller): add withReadonlyKeyring action

[ccharly]

Explanation

Add new action withReadonlyKeyring when we need to access a specific reading and read some data from it while being guarded by the global controller mutex.

This helps quite a bit with Snap account creation flow (especially on mobile) given that we need to access an HD keyring to derive keys.

References

N/A

Changelog

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes