[6.0 cherry-pick][embedded] Fix miscompile in IRGen in offset computation of Builtin.destroyArray

[kubamracek]

• Explanation: In Embedded Swift, we have custom IRGen code to handle init/take/copy/destroy of array builtins. We had a miscompile (a GEP uses to index into the individual elements of the array's storage is using the value's size and not the stride) that triggers for non-POD array element types where size!=stride (e.g. where the type is an enum with payloads). Fix is to fix the IRGen to emit a valid set of instructions to correctly index using the stride. [embedded] Fix miscompile in IRGen in offset computation of Builtin.destroyArray #73130
• Scope: Embedded Swift only.
• Risk: Low, all changes only apply to Embedded Swift.
• Testing: Added test case.
• Issue: rdar://126386301
• Reviewer: @eeckstein, @aschwaighofer on [embedded] Fix miscompile in IRGen in offset computation of Builtin.destroyArray #73130

[kubamracek]

@swift-ci please test