Refactor Apple version handling in the compiler

[madsmtm]

Move various Apple version handling code in the compiler out rustc_codegen_ssa and into a place where it can be accessed by rustc_attr_parsing, which I found to be necessary when doing #136867. Thought I'd split it out to make it easier to land, and to make further changes like #131477 have fewer conflicts / PR dependencies.

There should be no functional changes in this PR.

@rustbot label O-apple
r? rust-lang/compiler

[rustbot]

Failed to set assignee to t-compiler: invalid assignee

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[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[BoxyUwU]

r? compiler