Enable and optimize LSRA with APX push2/pop2

[anthonycanino]

APX allows to push/pop two registers from the stack with new push2 and pop2 instructions. This task is to enable this feature in the register allocator and tune/optimize.

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[DeepakRajendrakumaran]

@BruceForstall @kunalspathak @jakobbotsch I have been working on adding push2/pop2 support in JIT. We already have an issue tracking unwind changes at OS level(#112762). While we wait on that, I plan to go ahead and use push2/pop2 in Prolog/Eplilog with existing unwind code. For e.g., for push working on reg1 and reg2, this will look as follows.

                instGen_Push2Pop2(INS_push2, reg1, reg2);
                compiler->unwindPush(reg1);
                compiler->unwindPush(reg2);

Adding the comment here so that I can make any other changes required to handle this if others have any input here

[anthonycanino]

@JulieLeeMSFT this is completed with #116035. I will close and you may mark as completed on the master issue.