Partially fix mapping of virtual keys to characters

[lhecker]

Summary of the Pull Request

This PR mostly fixes the mapping of Alt combinations to unicode characters.

The case of AltGr was originally hotfixed by returning early in TerminalControl.
But this didn't fix e.g. AltShift combinations. See #2771 for instance.

This PR now fixes this particular remaining issue.
Cases where a single keypress generates more than a single UTF-16 code point (e.g. when diacritics come into play) are not fixed though, due to a limitation in the design of the low level KeyEvent class.

PR Checklist

• Closes
  • Closes Shift key not working properly in some situations #2771
  • Closes Alt+Shift+comma emit Alt + comma, it should emit Alt + [less than sign] #1819
  • Related Something wrong with keyboard modifiers processing? #1694 (Not sure about that one - I don't understand the issue description)
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Requires documentation to be updated
  • I changed the ITerminalInput interface
• 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: Shift key not working properly in some situations #2771

Detailed Description of the Pull Request / Additional comments

This removes the special handling of AltGr in TerminalControl, so that terminalInput may now handle it by itself.

I believe it'd be nice to extend InputTest.cpp to include a test for the translation of Shift. to ">", but unfortunately this would be exclusive to US keyboard layouts.
My german keyboard layout for instance uses Shift< for this (there's a dedicated "<" key).
How would I build a unit test for this that works independent of "internationalization"?

Validation Steps Performed

• Ensured that the expected behavior of Shift key not working properly in some situations #2771 can be observed.
• The special handling of AltGr is being removed in this PR.
  -> Ensured that AltGr combinations still work.

[lhecker]

@carlos-zamora I believe your review comments should be addressed now. 🙂

[lhecker]

I believe the tests are failing due to some recent commit in master? I don't think I caused these issues.

[DHowett-MSFT]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ghost]

This pull request has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 7 days. It will be closed if no further activity occurs within 7 days of this comment.

[lhecker]

@zadjii-msft @DHowett-MSFT This PR just got a No-Recent-Activity tag even though it's approved. 😕

[lhecker]

Ah, my comment removed the tag. 😄 Anyways… Do you know when (or if) this will be merged?

[zadjii-msft]

Whoops, that's on us. I think we were holding it since we were about to release v0.5, but now that 0.5 is out, let's get this in :)

[ghost]

🎉Windows Terminal Preview v0.5.2762.0 has been released which incorporates this pull request.:tada:

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