feat(test): Add support for regex in filter flag (#6343)

Currently, the documentation makes it sound like the test subcommand's filter
flag could accept some kind of pattern matching value like a glob or a regex,
although the function "createFilterFn" accepts a regex as an argument, there's
no way to pass an actual regex value from the CLI.

This commit makes it possible to pass a string that could be cast as regex 
when string matches "^/.*/$".

With this change, a user can use the filter flag as follow:

deno test --filter "/test-.+/"

Also tested that `\` get escaped properly, on MacOS at least, and this is 
also a valid flag:

deno test --filter "/test-\d+/"

1 files changed, 1 insertions, 0 deletions

diff --git a/cli/tests/unit/unit_tests.ts b/cli/tests/unit/unit_tests.ts
index 1701170d1..ad820a55c 100644
--- a/cli/tests/unit/unit_tests.ts
+++ b/cli/tests/unit/unit_tests.ts
@@ -24,6 +24,7 @@ import "./event_target_test.ts";
 import "./fetch_test.ts";
 import "./file_test.ts";
 import "./files_test.ts";
+import "./filter_function_test.ts";
 import "./form_data_test.ts";
 import "./format_error_test.ts";
 import "./fs_events_test.ts";