Disable model upload on Apple Silicon builds with user guidance

[bennettgoble]

The Apple Silicon viewer is ready for release but lacks model upload functionality due to missing ARM64 Havok library support. We should ship the native build anyway, as it has major performance benefits, but provide a graceful degradation path.

Requirements

1. Disable the "Build > Upload > Model..." menu item on Apple Silicon builds only
2. When clicked, display an alert dialog:

Model upload is not yet available on Apple Silicon, but will be supported in an upcoming release.
   
Workaround: Right-click the Second Life app in Finder, select
"Get Info", then check "Open using Rosetta"
   
[More Info] [OK]

3. "More Info" button should link to a wiki page explaining the limitation and Rosetta workaround in detai

Acceptance Criteria

• Model upload menu disabled on ARM64 builds only
• Alert displays correct platform-specific instructions
• No regression on Intel builds
• Wiki documentation page created

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[akleshchev]

Suggestion: while at it, also cover cases that have no havok or replacements with some generic 'no physics library, upload disabled'.

[Dan-Linden]

I ran 7.2.2.18110213724 in Rosetta mode and attempted to upload a mesh. It failed in the same way if fails on Apple Silicon mode.

[akleshchev]

It failed in the same way if fails on Apple Silicon mode.

Should we just show a 'Model upload is not yet available on Apple Silicon, but will be supported in an upcoming release.' warning?