test_runner: Add option to exclude empty lines from coverage report

# Feature Request: Add `--test-coverage-exclude-empty-lines` option to test runner ## Summary The Node.js test runner's coverage reporter (`--experimental-test-coverage`) reports empty lines and certain non-executable lines as "uncovered", leading to inaccurate coverage percentages. Other V8-based coverage tools like Vitest have solved this with an `ignoreEmptyLines` / `excludeEmptyLines` option. ## Problem When running tests with coverage using the native test runner: ```bash node --test --experimental-test-coverage tests/**/*.test.ts ``` Empty lines between statements are reported as uncovered: ``` # file | line % | branch % | funcs % | uncovered lines # parse.ts | 99.18 | 78.49 | 100.00 | 118 183-184 ``` Looking at line 118: ```typescript 116: // Find the element declaration for this root 117: const elementEntry = findElementByName(schema, rootLocalName); 118: 119: if (!elementEntry) { ``` Line 118 is **empty** - it contains no executable code, yet it's reported as uncovered. ## Expected Behavior Empty lines, comments, and TypeScript type-only lines should be excluded from coverage calculations, or there should be an option to exclude them. ## How Other Tools Solve This ### Vitest (`@vitest/coverage-v8`) Vitest uses `v8-to-istanbul` with the `excludeEmptyLines` option: - Issue: https://github.com/vitest-dev/vitest/issues/5423 - Implementation uses `@jridgewell/trace-mapping` to determine which lines contain runtime code ### v8-to-istanbul PR implementing this feature: https://github.com/istanbuljs/v8-to-istanbul/pull/244 The approach: > When source maps are available, use `@jridgewell/trace-mapping` to figure out which lines contain runtime code. If a line is not present in source maps, consider it as empty line. This will exclude TypeScript typings, comments, empty lines and any other special syntax that transpiled languages exclude from source maps. ### c8 c8 also uses v8-to-istanbul and can leverage the same `excludeEmptyLines` op…