* Add unused diagnostic subtype

Fixes #15710

Adds a new `DiagnosticTag` class that provide additional information about a diagnostic. Introduce `DiagnosticTag.Unnecessary` to mark when a diagnostic is for unused / unnecessary code

The design comes from Rosyln's diagnostic object and allows us to modify how a diagnostic is rendered without changing its serverity.

Hooks up JS and TS to use this new tag. This is controlled by the `javascript.showUnused.enabled` setting which is enabled by default

- Introduce a new diagnostic severity for unused.

    However, using this approach, if a user sets `noUnusedLocals` in their `tsconfig.json`, the resulting diagnostic could only show the squiggly OR be grayed out. Using `customTags` allows us to support both graying out and showing the squiggly

- Custom JS/TS implementation using decorators

    Not themable. We want a standard experience across languages.

* - Move to proposed
- Use numeric enum

There should be an API command to execute the color provider like we have for code complete and others. Fixes #45867

* Leverage notification progress support for progress API

fixes #44090

* only allow positive total/worked values

* drop total/worked in favour of percentage

* make sure to dispose CancellationTokenSource after use

* make the cancellation button optional

Fixes #10659

Allows workspace edits to also change files in the workspace

* Add CodeAction Type

Adds skeleton on a new CodeActionType and allows codeActionProvider to return either `Command`s or `CodeAction`s

Move proposed CodeAction API to proposed and try using it in TS

Split CodeAction into quickfix and refactoring classes

Update proposed interface

Update for new API

Adding basic docs

* Support workspace edits and text edits in codeactions

* Remove placeholders

* Resolving conflicts and making PR suggested changes

* Fix quick fix test

* Revert change to only use `CodeAction` instead of `CodeAction | Command` in modes since this will break `vscode.executeCodeActionProvider`

Fixes #35937