[SR-15093] Update availability diagnostic for macOS major version number changes

[beccadax]

Previous ID	SR-15093
Radar	None
Original Reporter	@beccadax
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, StarterBug
Assignee	isaac.s (JIRA)
Priority	Medium

md5: a76a5da1fc1aa7b153f4fc3280eab31e

Issue Description:

In TypeCheckAvailability.cpp, the function fixAvailabilityByNarrowingNearbyVersionCheck() checks if an availability specifier near the site of an error has a version that's very close to the one needed for that API, and if so, offers a fix-it for it.

"Very close" is defined as having the same major version number on most OSes, but for macOS, the minor version also has to match. This made sense a few years ago when macOS releases all had 10.x versions, but now that Apple is incrementing the major macOS version number regularly, it probably doesn't make sense anymore. So this condition should be tweaked to only apply if the major version number is 10.