[release/9.0] Fix CET debugger stepping over CALL instructions

[tommcdon]

Backport of #108809 to release/9.0

Customer Impact

• Customer reported
• Found internally

This fix addresses CET stepping issues found while testing .NET 9 apps under the debugger.

1. Resuming from a breakpoint on a CALL instruction triggers a CET failure, often seen as 0xc0000409 or Fail Fast. This can be reproduced by attempting to step through optimized code, such as a Ready-To-Run method.
2. Func-eval abort resulted in the process AV'ing.

Regression

• Yes
• No

Although the issue pre-exists, .NET 9 ships with CET enabled by default which will drastically increase the likelihood of customers encountering this issue..

Testing

VS Debugger validation. Manual validation stepping over call instructions, both with and without breakpoints set on them.

Risk

Medium-Low. It is a medium-sized code change but we have mitigated that risk by constraining the fix to a very narrow scenario which would result in a program crash without the fix. We will only perform an in-place single-step when CET debugging is enabled -and- when resuming from breakpoints on CALL instructions.

[jeffschwMSFT]

lgtm. please get a code review. we will take for consideration in 9 GA

[janvorli]

LGTM, thank you!