Ignore rule if file is dirty

[FunctionDJ]

Closes #2171.

Adds an unsavedOnly boolean property to eslint.rules.customizations entries. When true, the customization only applies while the file has unsaved changes; once saved, the rule reports at its original severity.

Motivating use case: eslint-plugin-prettier is useful in CI but noisy during active editing. With this option you can suppress prettier/prettier while typing while still seeing violations in committed/saved code:

"eslint.rules.customizations": [
  { "rule": "prettier/prettier", "severity": "off", "unsavedOnly": true }
]

Implementation notes:

Dirty state is tracked server-side by recording the document version at open/save (textDocument/didOpen, textDocument/didSave) and comparing against the current version. This avoids a false-dirty state that would arise from using TextDocuments.onDidChangeContent, which fires for both didOpen and didChange notifications.

Because the pull diagnostics model doesn't automatically re-pull after a save when in-memory content is unchanged, onDidSave triggers connection.languages.diagnostics.refresh() so the updated dirty state is reflected immediately.

The RuleSeverities cache key is extended with the dirty flag (ruleId:0/1) so clean and dirty results are cached independently and invalidated correctly on settings change.

Human written AI Disclaimer: I used Copilot to help me with this implementation and the above PR text body, but I reviewed it, ran the mocha tests, used the Launch Config to test it, and iterated on the feature until it actually worked with Launch Config. I take responsibility for this code. I also looked into if there's a simpler way to determine if a document is dirty, but according to Copilot this would require a client-server roundtrip that's not necessary when the implementation in this PR also works server-side-only.

[FunctionDJ]

@microsoft-github-policy-service agree