Support Tahoe, drop Mojave and older

[p-linnane]

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This PR marks macOS Tahoe 26 as officially supported, and drops support for macOS Mojave 10.14 and older.

Marking as draft until we are satisfied that mass bottling has progressed enough.

[MikeMcQuaid]

Good to ship whenever you're happy with this @p-linnane!

[fxcoudert]

I think we're ready to merge this