Rewrite relative import extensions with flag

[andrewbranch]

This PR adds --rewriteRelativeImportExtensions to support transforming module specifiers from e.g. "./utils.ts" to "./utils.js". A module specifier in an import declaration, export declaration, or import assignment (import foo = require("...")) will be rewritten during JS emit if it meets all of these criteria:

• it begins with ./ or ../
• it does not end in a declaration file name (.d.ts, .d.mts, .d.cts, .d.*.ts)
• it ends in .ts, .tsx, .mts, or .cts

Errors are issued in an attempt to catch common mistakes:

• A module specifier will get rewritten but will break after rewriting:
  • "./foo.ts" actually resolves to ./foo.ts.ts or foo.ts/index.ts
  • "../other-project/src/index.ts" belongs to another project where outputs go to a different outDir
• A module specifier will not get rewritten but will break after emitting as-is:
  • "#blah/foo.ts" resolves to foo.ts where the .ts matches through a wildcard

TODO:

• Rewriting/shimming of async import
• Rewriting/shimming of require in JS input files?

Fixes #59597

[andrewbranch]

@typescript-bot pack this

[typescript-bot]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
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[typescript-bot]

Hey @andrewbranch, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/163457/artifacts?artifactName=tgz&fileId=2225118E5057943A4B80A3A9D8FE2EA5696226BA40FE09011C7C2241BF80844302&fileName=/typescript-5.7.0-insiders.20240826.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

[typescript-bot]

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page.

Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up.

[andrewbranch]

@typescript-bot pack this

[typescript-bot]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
pack this	✅ Started	✅ Results

[typescript-bot]

Hey @andrewbranch, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/163603/artifacts?artifactName=tgz&fileId=366D2974C150D261A1702BA0C2511DBAF6432824433FEBBEB4D1A438DE1953C602&fileName=/typescript-5.7.0-insiders.20240917.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;