Add a `re()` method to the `Filter` class.

Callers shouldn't have to duplicate the regular expressions.

Note that the name of the method is consistent with the name
of the property in the `_Match` class.

Change-Id: If418f820fd6d460cfa4d90f8a837f1cb7994608d
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61170
Reviewed-by: Perry Lorier <perryl@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
3 files changed