Motivation for features / changes

Part of a step-by-step Angular migration from v16 to v22. This PR upgrades the frontend from Angular 19 to Angular 20.

Technical description of changes

• Updated all @angular/* packages to ^20.0.0 (resolved 20.3.25 in yarn.lock), @ngrx/* to ^20.0.0, and TypeScript to 5.8.3
• Pinned @angular/build-tooling to the Angular 20.0.0 stable commit (b87de6c1) and renamed the patch file to match the new internal version string
• Added aspect_rules_js v2.1.0 to WORKSPACE. It is required by the updated build-tools spec-bundling rules, which now use JsInfo providers from that ruleset.
• Fix karma web test suite for Angular 20 upgrade
  • Updated @io_bazel_rules_webtesting from browsers-0.3.3 to browsers-0.3.4 to upgrade Chromium from Chrome 94 to Chrome 123
  • Added custom browser target at tensorboard/tools/browsers since the default alias has restricted visibility and cannot be used from TensorBoard targets
  • Changed spec_bundle target to es2021 since Chrome 123 crashes on ES2022 class static blocks emitted by Angular npm packages.
  • Skipped WebGL tests with pending() since Chrome 123 headless on macOS ARM64 has no GPU and ThreeRenderer throws on class construction.
  • Fixed tests that relied on ng-reflect-* attributes removed in Angular 20, now reading from componentInstance or nativeElement instead.
  • Updated formatter test since Chrome 123 ICU library changed the en-US date time separator.

Detailed steps to verify changes work correctly (as executed by you)

Alternate designs / implementations considered (or N/A)