fix(@schematics/angular): preserve the workspace build version during migration

[raashish1601]

Summary

• reuse the workspace version of @angular-devkit/build-angular when the use-application-builder migration adds @angular/build
• fall back to an existing @angular/build version if it is already present, and only then fall back to the repo default
• add a regression spec covering an 18.2.x workspace so the migration no longer upgrades the package to an incompatible 20.x release

Testing

• corepack pnpm exec prettier --check packages/schematics/angular/migrations/use-application-builder/migration.ts packages/schematics/angular/migrations/use-application-builder/migration_spec.ts
• corepack pnpm exec eslint packages/schematics/angular/migrations/use-application-builder/migration.ts packages/schematics/angular/migrations/use-application-builder/migration_spec.ts
• git diff --check
• corepack pnpm -s ng-dev format staged
• attempted corepack pnpm bazel test //packages/schematics/angular:test --lockfile_mode=update --test_output=errors --verbose_failures under portable Node v24.13.1 with BAZEL_SH pointed at Git Bash; the target analyzed successfully but the Windows host then failed in Bazel's TypeScript toolchain before the schematic suite ran because the expected aspect_rules_js TypeScript entry point was missing from the generated execroot

Fixes #30696

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[gemini-code-assist]

Code Review

This pull request updates the use-application-builder migration to reuse the existing version of the builder when migrating to @angular/build. It introduces logic to check for the current version of @angular-devkit/build-angular or @angular/build in the package.json and uses that version for the new @angular/build dependency, falling back to a default version if neither is found. A new test case has been added to verify this version preservation. I have no feedback to provide.

[alan-agius4]

See comment

[alan-agius4]

Suggested change

	const buildDependency =
	getPackageJsonDependency(tree, '@angular-devkit/build-angular') ??
	getPackageJsonDependency(tree, '@angular/build');
	rules.push(
	addDependency('@angular/build', latestVersions.DevkitBuildAngular, {
	addDependency('@angular/build', buildDependency?.version ?? latestVersions.AngularBuild, {
	type: DependencyType.Dev,
	existing: ExistingBehavior.Replace,
	}),
	const buildAngularVersion =
	getDependency(tree, '@angular-devkit/build-angular')?.version ??
	latestVersions.DevkitBuildAngular;
	rules.push(
	addDependency('@angular/build', buildAngularVersion, {
	type: DependencyType.Dev,
	existing: ExistingBehavior.Skip,
	}),

[raashish1601]

Applied in 60392dd. I switched to getDependency(...), used latestVersions.DevkitBuildAngular as the fallback, kept ExistingBehavior.Skip, and added coverage for preserving an existing @angular/build version.

[alan-agius4]

Please sign the CLA and squash the commits. Thanks

[alan-agius4]

NIT

Suggested change

	latestVersions.DevkitBuildAngular;
	latestVersions.AngularBuild;