Remove getcontext and setcontext usage (#9759)

Remove getcontext and setcontext usage (#9759)

It turns out that the getcontext and setcontext that I have used in my stack
oveflow reporting change are not present e.g. on Alpine Linux or on Android.
So I am replacing their usage with RtlCaptureContext and RtlRestoreContext
instead.

I have also found that the addition of the .cfi_adjust_cfa_offset to the
PROLOG_SAVE_REG_PAIR has broken unwinding of all helpers that use
PROLOG_WITH_TRANSITION_BLOCK, because the PROLOG_STACK_ALLOC macro
updates the CFA offset. So I am fixing that by removing the CFA offset
updating from the PROLOG_STACK_ALLOC and adding explicit one to the
ARM64 CallSignalHandlerWrapper.