[Mentions v2] Add new rule in ExpensiMark for room mentions

[robertKozik]

Important

Room mentions consists of # symbol followed by room name. Room name consist of any char sequence connected by hyphens (no spaces is allowed inside room name)

Fixed Issues

$ Expensify/App#39538

Tests

1. What unit/integration tests cover your change? What autoQA tests cover your change?
   I've created multiple unit tests to cover most of the possible usages of room/report mentions. Room mentions consists of # symbol followed by room name
2. What tests did you perform that validates your changed worked?
   Check if existing unit tests are not failing after my. changes, added additional tests to cover room mentions

QA

1. What does QA need to do to validate your changes?
   Room mentions are not yet visible inside E/App, so to validate this changes we should only check for regressions or other markdown rules
2. What areas to they need to test for regressions?
   Room mention syntax is very similar to Heading syntax. Extensive testing of this aspeect of markdown parser is recommended. Moreover all other markdown rules should be untouched

[robertKozik]

Thanks @rlinoz, I've added tests and comment

[Beamanator]

Can we also add at least 1 test for room names with - since that will probably be a pretty common use-case? Ex: #room-name, maybe even #room-123

[Beamanator]

Looking good to me!