@actions/tool-cache: convert to an ESM module

[danwkennedy]

Description

We're upgrading all the packages in this repo to ESM modules. @actions/tool-cache can go next since all its dependencies are ESM modules.

[Copilot]

Pull request overview

This PR migrates @actions/tool-cache to be an ESM-only package, aligning it with other ESM-converted packages in the repo and updating its dependencies accordingly.

Changes:

• Configure the tool-cache TypeScript build for Node-style ESM (module/moduleResolution set to node16) and update internal imports to use .js specifiers and top-level @actions/exec exports.
• Refactor manifest.ts to pure ESM imports and introduce an _internal helper object for testability, while keeping _readLinuxVersionFile as a backwards-compatibility alias.
• Mark the package as ESM-only in package.json, add an exports map, bump to version 4.0.0 with updated dependency versions and lockfile, update Jest config and tests to work with the new ESM shape, and document the breaking change in RELEASES.md.

Reviewed changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/tool-cache/tsconfig.json	Sets module and moduleResolution to node16 for ESM-compatible builds while preserving existing outDir/rootDir layout.
packages/tool-cache/src/tool-cache.ts	Updates internal imports to use .js specifiers and the top-level @actions/exec ESM entrypoint, keeping public API and logic unchanged.
packages/tool-cache/src/manifest.ts	Converts from require-style imports to ESM imports, introduces _internal.readLinuxVersionFile for Jest mocking, and retains _readLinuxVersionFile() as a compatibility wrapper.
packages/tool-cache/package.json	Declares the package as ESM-only via "type": "module", adds an exports map for types/import, bumps to 4.0.0, and updates runtime and dev dependencies to current major versions.
packages/tool-cache/package-lock.json	Synchronizes lockfile with new dependency versions (including transitive dev tooling like nock and its dependencies).
packages/tool-cache/__tests__/tool-cache.test.ts	Adjusts imports to reference ../src/tool-cache.js so tests run against the ESM-shaped source with Jest’s .js mapper.
packages/tool-cache/__tests__/retry-helper.test.ts	Points the test to ../src/retry-helper.js to match ESM-style internal imports.
packages/tool-cache/__tests__/manifest.test.ts	Switches to ESM-style imports for tool-cache/manifest and updates spies to target mm._internal.readLinuxVersionFile, keeping the OS-version resolution tests working.
packages/tool-cache/RELEASES.md	Adds a 4.0.0 entry documenting that the package is now ESM-only and clarifies the require vs import() breaking change.
jest.config.js	Maps @actions/tool-cache to the built lib/tool-cache.js and ensures it and its dependencies are transpiled by ts-jest, mirroring the setup used for other ESM-converted packages.

Files not reviewed (1)

• packages/tool-cache/package-lock.json: Language not supported

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