[CP][stable channel] Ensure start/stop file watching requests are run on the dart thread.

[devoncarew]

commit(s) to merge: ed82bb6

merge instructions: clean merge or patch CL

• assumed clean

What is the issue: Brief description of the problem

• numerous user reports of the analysis server stopping responding to IDE requests; this is due to the isolate running the analysis server deadlocking when unsubscribing from file watching events

What is the fix: Brief description of the fix

At present start/stop requests are scheduled on RunLoop thread. This results in deadlocks since same RunLoop thread might be busy with blocking writes of file watching events, not giving a chance for Dart to read previously-written events. Reading would unblock writer.

This fix moves start/stop requests to run on Dart thread instead.

Why cherrypick: Describe the reasons, like many users impacted, or serious functional issues, for example

• lots of users reports; likely manifesting in a few separate issues

Risk:

• assumed low; cc @a-siva @aam

Link to original issue(s):

• (macos) Analyzer sometimes stops responding in VSCode when mass file change events occur #45996

/cc @kevmoo @mit-mit @whesse @athomas @vsmenon @franklinyow @a-siva @aam @DanTup

[franklinyow]

Description:
Fix for analysis server stop responding to IDE requests , see #45996 for detail

[aam]

@mraleph pointed out potential (unlikely) problem in the original fix, which were fixed in follow-up dart#202312 landed three days ago in dart sdk.

[aam]

that follow-up change I mentioned dart#202312 landed in flutter flutter/flutter@c9d5485 21h ago

[a-siva]

Created #46298 for the additional change to be picked.

[athomas]

Merged to stable in 516eb3b (2.13.3).