Cascade code actions on save by provider

[Vivek JM (vivekjm)]

Fixes #174295

Code action providers used for save participants were queried concurrently against the same document version, but their edits were then applied sequentially. When multiple import organizers returned edits, the later provider could apply stale offsets and duplicate or corrupt imports.

This queries and applies providers sequentially in the registry's deterministic order. Each provider therefore sees the document after the preceding provider's edits, while action ordering within a provider remains unchanged.

Tests run:

• npm run typecheck-client
• npm run gulp compile (0 errors)
• Save Participants suite (6 passing), including a regression that reproduced the duplicate import before the fix
• CodeAction suite (7 passing)
• Targeted ESLint, pre-commit hygiene, and diff checks

[Copilot]

Pull request overview

Cascades editor code actions on save so each provider sees prior edits.

Changes:

• Adds provider-specific code-action querying.
• Applies save actions sequentially by provider.
• Adds a regression test for import corruption.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
codeAction.ts	Adds optional provider filtering.
saveParticipants.ts	Serializes providers during editor saves.
saveParticipant.test.ts	Tests cascading import organizers.