fix: Declared mrmime as a runtime dependency (20.3.x)

[Ionaru]

Fixes #100 for the 20.x line (same fix as #104)

packages/angular/src/builders/build/builder.ts and packages/angular/src/plugin/index.ts import mrmime at runtime, but the hand-curated dependencies list in packages/angular/package.json never included it (only the workspace root manifest did, which is why local development never noticed). The import only resolved while another installed package happened to hoist mrmime (typically the v3 mainline package left in place during migration), and ng build fails with Cannot find package 'mrmime' once that is uninstalled.

This adds mrmime to the publishable manifest's dependencies, matching the mainline package. Verified locally: nx build angular-adapter now emits packages/angular/dist/package.json with mrmime under dependencies, and the test target passes.

Note on scope: esbuild and json5 are also imported at runtime without being declared (as are @schematics/angular and @nx/devkit in the schematics and generator entry points). Those are deliberately not added here because they are highly likely to be already installed through Angular's own dependencies (@angular/build, @angular-devkit/*), unlike mrmime, which nothing else in an Angular workspace provides.