Support any number of leading zeros in VT parameter values

[j4james]

Summary of the Pull Request

Adds support for any number of leading zeros in the parameter values of VT escape sequences. Tested manually, with Vttest, and with unit tests.

PR Checklist

• Closes Parameter values of more than 5 digits are not supported #358
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: Parameter values of more than 5 digits are not supported #358

Detailed Description of the Pull Request / Additional comments

In the StateMachine::_ActionParam and StateMachine::_ActionOscParam methods, the parser would treat any parameter number with more than 5 digits as being the maximum value. This PR add checks which prevent leading zeros from contributing to that count, so the 5 digit limit now only applies to significant digits.

Validation Steps Performed

• I've tested in the WSL bash shell with escape sequences containing many leading zeros, e.g.:
  printf "\033[0000000032mGREEN?\033[m\n".
• I've confirmed that the leading zeros test in Vttest now works (the last screen in the Test of cursor movements).
• I've added a couple of unit tests in Microsoft::Console::VirtualTerminal::OutputEngineTest for both the CSI and OSC sequences.

[zadjii-msft]

Great work!

[DHowett-MSFT]

This looks great. Thank you!

[DHowett-MSFT]

Hey, this just went out in the inbox windows console with insider build 18932! Congrats!