babel --watch should have equivalent file selection logic with babel

[JLHwung]

Q	A
Fixed Issues?	Fixes #10270
Patch: Bug Fix?	Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Nope
Documentation PR Link
Any Dependency Changes?
License	MIT

In this PR, we align file selection logic of --watch to one time building. In

babel/packages/babel-cli/src/babel/file.js

Lines 144 to 163 in f08062b

	filenames.forEach(function(filename) {
	if (!fs.existsSync(filename)) return;
	const stat = fs.statSync(filename);
	if (stat.isDirectory()) {
	const dirname = filename;
	util
	.readdirForCompilable(
	filename,
	cliOptions.includeDotfiles,
	cliOptions.extensions,
	)
	.forEach(function(filename) {
	_filenames.push(path.join(dirname, filename));
	});
	} else {
	_filenames.push(filename);
	}
	});

The cli options --extensions is used to filter compilable files if the filename argument is a directory. However the watch logic excludes all non-compilable files even if it is specified in filename argument.

We also introduce minor performance tweak by passing disableGlobbing: true into chokidar as @babel/cli does not support globbing.

Fixture-based unit test does not work here since we need separate process to trigger a file change.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/11266/

[nicolo-ribaudo]

@JLHwung Could you rebase and merge?