[license-tool] Generate `.d.ts` declaration files and remove `src/` from published package

[olexii4]

Is your enhancement related to a problem? Please describe

The published npm package @eclipse-che/license-tool ships the entire src/ directory alongside dist/, inflating the tarball unnecessarily.

The root cause: the webpack build uses transpileOnly: true in ts-loader, so no .d.ts declaration files are emitted into dist/. The "types": "dist/index.d.ts" field in package.json points to a file that does not exist. Including src/ in the files array is a workaround to give TypeScript consumers access to type information via source files.

Current state:

• package.json declares "types": "dist/index.d.ts" — this file does not exist
• package.json "files" includes "src" — ships raw TypeScript source to compensate
• TypeScript consumers cannot get proper type-checking from dist/

Describe the solution you'd like

Generate .d.ts declaration files during the build and remove src/ from the published package.

Implementation

1. Add a postbuild step to emit declarations:

"postbuild": "tsc --emitDeclarationOnly --outDir dist && chmod +x dist/cli.js"

2. Remove src from the files array:

"files": [
  "dist"
],

3. Verify that dist/index.d.ts is generated after npm run build.

Expected result

• dist/index.d.ts exists and provides correct type information for library consumers
• src/ is no longer shipped in the npm tarball
• Package size is reduced
• "types": "dist/index.d.ts" in package.json resolves correctly

Describe alternatives you've considered

• Keep shipping src/ — works but inflates the tarball and is non-standard
• Use tsc instead of webpack — would generate declarations natively, but loses webpack bundling benefits (tree-shaking, single-file output, banner plugin for CLI shebang)

Additional context

Found during CHE-23756 PR review.