[mono] Fix SwiftError variable offset calculation

[kotlarmilos]

Description

This PR attempts to fix CryptoKit test failure encountered in #102583. The current approach always allocates a local var for SwiftSelf and doesn't set correct offset when the argument is passed via the stack to the wrapper.

The idea is to allocate a new stack var for SwiftError only when it is passed to the wrapper via regs. If SwiftError is passed to the wrapper via the stack, the existing stack var could be used, instead of a local variable.

In the wrapper prologue, if SwiftError is passed to the wrapper via regs, its value should be preserved in a local variable.

This is determined by checking ainfo->offset which is set in get_call_info. On amd64, if SwiftError is passed via regs, inreg is set to FALSE and is handled in the common block for all reg arguments. Reverse pinvoke wrappers should always allocate the local variable, as the pinvoke flag in get_call_info is 1, whereas for direct pinvoke, it is 0.

Validation

These changes should be verified using the Interop/Swift runtime tests and the Security.Cryptography library tests.

[kotlarmilos]

/azp run runtime-extra-platforms

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[kotlarmilos]

/azp run runtime-extra-platforms

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[kotlarmilos]

/azp run runtime-extra-platforms

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[kotlarmilos]

@matouskozak @jkurdek Please take a look at these changes.

[matouskozak]

The changes LGTM! and overall the code looks much cleaner to me know.

[jkurdek]

Looks good to me!