build: update vitest monorepo to v5

[alan-agius4]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

• Vitest and associated @vitest/* packages are on v4.
• Vitest E2E tests install hardcoded major versions of Vitest, Playwright, WebdriverIO, and coverage packages via installPackage, which can lead to version mismatches when upgrading Vitest.
• The splitting option in @angular/build:unit-test was introduced to work around an issue in Vitest 4 where shared-module exports in class-field initializers were uninitialized under JSDOM when code splitting was enabled.
• Generated Vitest config used .ts extension which produced ESM warnings in projects without "type": "module".
• Inline projects in Vitest 5 default to extends: true, which caused array options like browser.instances to be concatenated twice.

What is the new behavior?

This PR updates the Vitest monorepo dependencies to v5 and takes over #34030 with the following changes:

1. build: update vitest monorepo to v5

   • Updates Vitest monorepo packages (vitest, @vitest/browser-*, @vitest/coverage-*) to v5.0.0.
   • Updates latest-versions package definitions accordingly.

2. test: resolve vitest dependencies from latest-versions in e2e tests

   • Refactors applyVitestBuilder to dynamically resolve dependency versions directly from @schematics/angular/utility/latest-versions/package.json and install them in a single batch using installWorkspacePackages.
   • Updates all Vitest E2E test suites to pass dependency options (playwright, coverageV8, coverageIstanbul, webdriver) directly to applyVitestBuilder, eliminating hardcoded major version installations.

3. refactor(@angular/build): deprecate splitting option in unit-test builder

   • Marks the splitting option in schema.json as deprecated (x-deprecated: "No longer needed with Vitest 5."). Disabling code splitting is no longer necessary with Vitest 5, as the shared chunk initialization issue under JSDOM has been resolved.
   • Removes the splitting: false workaround from vitest-shared-chunk-init_spec.ts.

4. refactor(@schematics/angular): use .mts extension for generated Vitest configuration

   • Generates vitest-base.config.mts instead of .ts to ensure Node.js treats it as ESM regardless of workspace package type.
   • Updates related schematics, karma migration hints, and tests.

5. fix(@angular/build): disable root config extension for inline test project

   • Sets extends: false on the inline project configuration in the Vitest configuration plugin. Since the Angular CLI test runner already explicitly merges user-provided options into projectConfig, disabling automatic root config extension prevents duplicate browser instances and repeated test executions in Vitest 5.

6. build: update @vitest/browser-webdriverio to 5.0.0-rc.1

   • Updates @vitest/browser-webdriverio to ^5.0.0-rc.1 in latest-versions.
   • Drops { force: true } in Vitest E2E package installation.

Does this PR introduce a breaking change?

• Yes
• No

[gemini-code-assist]

Code Review

This pull request upgrades Vitest and its associated packages from version 4 to 5.0.0 across the workspace. It updates default configuration files to use the .mts extension, deprecates the splitting option in the unit-test schema, and refactors E2E tests to utilize a centralized helper for installing Vitest-related dependencies. Additionally, it introduces platform-specific test filtering in the E2E runner. A review comment highlights an issue in the new Vitest v4 compatibility test, which incorrectly uses the Vitest v5 playwright() configuration API alongside Vitest v4 dependencies.