test: documentation for E2E testing and syncing local Angular changes

[Zac-Smucker-Bryan]

While working on e2e tests in the angular directory, I encountered a few documentation issues in the ionic-framework repo (not docs) that made the local development workflow more difficult to follow.

• The "See Ionic's E2E testing guide" link in CONTRIBUTING.md resolves to a 404 when viewed from GitHub's Contributing tab because the relative path is not resolved correctly.

  • Broken link: https://github.com/ionic-team/ionic-framework/blob/core/src/utils/test/playwright/docs/README.md
  • Intended destination: https://github.com/ionic-team/ionic-framework/blob/main/core/src/utils/test/playwright/docs/README.md

• The Angular testing guide (docs/angular/testing.md) seems to omits some steps that are necessary to successfully test local framework changes, including:

  • Removing existing npm link relationships before starting a new sync cycle.
  • Building packages/angular-server each time.
  • Installing Playwright browser dependencies before running Playwright tests for the first time.

This is the workflow that I used to sync my changes consistently to while working on a test in form.spec.ts:
`0. Make sure there are no lingering npm links
npm unlink *

1. Build @ionic/core
   cd core && npm install && npm run build && cd ..

2. Build @ionic/angular
   cd packages/angular && npm install && npm run build && cd ../..

3. Build @ionic/angular-server
   cd packages/angular-server && npm install && npm run build && cd ../..

4. Merge base + ng20 into the build directory
   cd packages/angular/test && ./build.sh ng20

5. Install test app dependencies
   cd build/ng20 && npm install

6. Install local builds via pack
   npm run sync

7. Install Playwright browsers (first time only)
   npx playwright install chromium

8. Run the specific test
   npx playwright test e2e/src/lazy/form.spec.ts
   `