fix(@angular/build): exclude only source test files with unit-test vitest support

When using the experimental unit-test builder with the vitest runner and code coverage,
the automatic coverage excludes are now adjust to not include the bundled test files.
This previously prevent accurate coverage analysis.
Vite does this as a convenience but is problematic for the bundling strategy employed by the
builder's test setup. To workaround this, the excludes are adjusted here to only automatically
exclude the TypeScript source test files.

(cherry picked from commit 87f4121)

Author: clydin

packages/angular/build/src/builders/unit-test/builder.ts

@@ -230,11 +230,25 @@ export async function* execute(
           reporters: normalizedOptions.reporters ?? ['default'],
           coverage: {
             enabled: normalizedOptions.codeCoverage,
-            exclude: normalizedOptions.codeCoverageExclude,
             excludeAfterRemap: true,
           },
           ...debugOptions,
         },
+        plugins: [
+          {
+            name: 'angular-coverage-exclude',
+            configureVitest(context) {
+              // Adjust coverage excludes to not include the otherwise automatically inserted included unit tests.
+              // Vite does this as a convenience but is problematic for the bundling strategy employed by the
+              // builder's test setup. To workaround this, the excludes are adjusted here to only automatically
+              // exclude the TypeScript source test files.
+              context.project.config.coverage.exclude = [
+                ...(normalizedOptions.codeCoverageExclude ?? []),
+                '**/*.{test,spec}.?(c|m)ts',
+              ];
+            },
+          },
+        ],
       });
 
       // Check if all the tests pass to calculate the result