fix(@schematics/angular): keep base test build options in per-configuration Karma migration

[MeAkib]

The Karma to Vitest migration moves build-only test options such as styles into a testing build configuration and points the test target at it. For each test configuration it created a separate testing-<name> build configuration containing only that configuration's own options. Because a test configuration's buildTarget replaces the base one, running ng test --configuration <name> lost the options moved from the base test options.

Merge the base options into each per-configuration build configuration, with the configuration's own values taking precedence.

[gemini-code-assist]

Code Review

This pull request updates the Karma to Vitest migration schematic to correctly handle inheritance of base test options in per-configuration build settings. It ensures that custom build options are properly merged, preventing potential configuration loss. The review feedback highlights a potential issue with spreading undefined base options and provides a safer implementation using a guard clause.

[gemini-code-assist]

If customBuildOptions[''] is undefined (which can happen if the test target has no base options defined), spreading it directly in { ...customBuildOptions[''], ...configOptions } might lead to potential issues or TypeScript compilation errors depending on the compiler settings (such as noUncheckedIndexedAccess). Adding a guard to ensure customBuildOptions[''] is defined before spreading is safer and more robust.

Suggested change

	const mergedOptions = configKey
	? { ...customBuildOptions[''], ...configOptions }
	: configOptions;
	const mergedOptions = configKey && customBuildOptions['']
	? { ...customBuildOptions[''], ...configOptions }
	: configOptions;

[thekhegay]

styles case is fixed but aot comes back - processTestTargetOptions seeds every config entry with { aot: false, optimization: false, extractLicenses: false }, so seeded aot: false of ci wins over explicit aot: true from base here
test options { styles, aot: true } + ci: { watch: false } gives testing with aot: true and testing-ci with aot: false, so ng test runs AOT and ng test -c ci runs JIT. same for optimization and extractLicenses
new spec doesnt set aot so it passes either way
seeding Karma defaults only for base entry looks enough, configs then get them through this merge (checked on 22.3.0-next.2 with it patched in):

customBuildOptions[configKey] = configKey
  ? {}
  : {
      aot: false,
      optimization: false,
      extractLicenses: false,
    };