refactor[scripts/prettier]: respect .prettierignore when resolving js files via glob (#27627)

This script is used on CI in `yarn_lint` job. With current `glob` call
settings, it includes a bunch of build files, which are actually ignored
by listing them in `.prettierignore`. This check is not failing only
because there is no build step before it.

If you run `node ./scripts/prettier/index` with build files present, you
will see a bunch of files listed as non-formatted. These changes add a
simple logic to include all paths listed in `.prettierignore` to ignore
list of `glob` call with transforming them from gitignore-style to
glob-style.

This should unblock CI for https://github.com/facebook/react/pull/27612,
where `flow-typed` directory will be added, turned out that including it
in `.prettierignore` is not enough.