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## Summary of the Pull Request
Adds a simple helper function to look up the GUID associated with a profile name.
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## References
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## PR Checklist
* [x] Closes#3680
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Tests added/passed. Yes, new test group in `SettingsTests`!
* [ ] Requires documentation to be updated
* [x] 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: #3680
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## Detailed Description of the Pull Request / Additional comments
Very simple function, for-each through profiles checking for a match. Returns the associated GUID if found, else returns the null GUID.
This function is marked as `noexcept` to comply with assumption made by other `CascadiaSettings` functions that [`Profiles::GetGuid`](https://github.com/microsoft/terminal/blob/master/src/cascadia/TerminalApp/Profile.cpp#L141) does not throw, despite it throwing.
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## Validation Steps Performed
The new function is simple and can be visually validated, but added tests regardless. A new test group was added in `SettingsTests` called `TestHelperFunctions` to validate the new function `FindGuid` and older function `FindProfile`. This test group could be used to validate more helper functions in `CascadiaSettings` as they're added. The new test group passes after running `te.exe TerminalApp.LocalTests.dll`.
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* Added FindGuid helper function
* Style change
* Tests for FindGuid and FindProfile
* Fixed code format?
* Code format guess
No feedback from the Azure pipeline
* optional<GUID> fix
* Updated function desc
e9a3fe5578