Improve codegen of funclet prologs

[filipnavara]

PR #114630 eliminated the PSPSym from CoreCLR ABI. This means that some parts of stack layout no longer need to be in sync between the main function and the funclets.

Notably, two of them were mentioned in comments and should be investigated for removal:

• Extra space in ARM64 prolog for varargs to align the relative offset of the now non-existent PSPSym (Abolish PSPSym from ABI #114630 (comment))
• Saved/restored registers on ARM64 (Abolish PSPSym from ABI #114630 (comment))

It's possible that other architectures may contain similar vestiges.

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[AndyAyersMS]

There is also some extensive padding in arm64 OSR for PSP which looks like it will no longer be needed: see #62831 (comment)

[filipnavara]

There is also some extensive padding in arm64 OSR for PSP

I believe I already removed all the extra padding specific to the OSR frames.

[JulieLeeMSFT]

CC @kunalspathak.