Renamed and reimplemented GetFromRegistryProgramThatOpensFileType

[tombogle]

Renamed GetFromRegistryProgramThatOpensFileType to GetDefaultProgramForFileType and implemented it in a way that works on Windows 11, Mono (probably) and MacOS (untested).

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This change is 

[github-actions]

LibPalaso Tests

    45 files  ±0      45 suites  ±0   12m 26s ⏱️ +31s
 4 830 tests ±0   4 599 ✅ ±0  231 💤 ±0  0 ❌ ±0 
14 008 runs  ±0  13 381 ✅ ±0  627 💤 ±0  0 ❌ ±0 

Results for commit 00528d3. ± Comparison against base commit de37405.

This pull request removes 3 and adds 3 tests. Note that renamed tests count towards both.

SIL.Tests.IO.FileLocatorTests ‑ GetFromRegistryProgramThatOpensFileType_SendExtensionWithoutPeriod_ReturnsProgramPath
SIL.Tests.IO.FileLocatorTests ‑ GetFromRegistryProgramThatOpensFileType_SendInvalidType_ReturnsNull
SIL.Tests.IO.FileLocatorTests ‑ GetFromRegistryProgramThatOpensFileType_SendValidType_ReturnsProgramPath

SIL.Tests.IO.FileLocatorTests ‑ GetDefaultProgramForFileType_SendExtensionWithoutPeriod_ReturnsProgramPath
SIL.Tests.IO.FileLocatorTests ‑ GetDefaultProgramForFileType_SendInvalidType_ReturnsNull
SIL.Tests.IO.FileLocatorTests ‑ GetDefaultProgramForFileType_SendValidType_ReturnsProgramPath

[josephmyers]

Note that, given the test project targets .NET8, you could easily test Linux (not Mono) if you have access to it. I think a one-time verification for this PR would be beneficial, if possible. Other than that, the code here looks good to me

[tombogle]

I don't have a Linux machine. In some theoretical world, I could probably spin up a VM, but I doubt I'd ever got to it. I agree that it would be ideal.