Add translations for string.Substring with one arg

[stevendarby]

Fixes #20173

[dnfadmin]

All CLA requirements met.

[stevendarby]

Sorry for delay on this, as a first timer I’m just waiting on a confirmation around the two options on the CLA, should end up fine either way. CLA signed

[stevendarby]

@ajcvickers Let me know if there’s anything else I need to do to unblock this.

[smitpatel]

Since these are in projection so for cosmos/sqlite just pass even though not translating. We should add tests where they are used in where. @maumar will provide guidance on that.

[stevendarby]

Thanks, I think I had a misconception that abstract class tests weren’t discovered.

I’ll take a closer look and can make a start improving the testing as suggested.

[stevendarby]

• Decided to just go ahead and implement for Cosmos and Sqlite too.
• Sqlite doesn't need 3rd argument so don't have to do a length function
• Tests now use the substring in the where.
• the substring with IndexOf test started to break, but wasn't sure why - seemed to be problem in the test framework? Appreciate any help there. For now I removed as only had that one after basing tests on the 'two arg' substring, perhaps it isn't really needed in the substring tests.
• Happy to take any further guidance, hopefully this is a step in the right direction though.

[smitpatel]

@stevendarby - thank you for contribution.