[clr-interp] Fix EmptyThisCall test

[davidwrighton]

• Add detection for attempting to call function with this call calling convention without actually passing a this argument.

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[janvorli]

LGTM, thank you!

[Copilot]

Pull request overview

This PR adds validation to detect an invalid scenario in the CoreCLR interpreter where a function using an instance method calling convention (such as thiscall, CMemberFunction, etc.) is called with zero arguments. Instance method calling conventions require at least one argument (the 'this' pointer), so calling such a function with zero arguments is invalid code.

Key changes:

• New validation function CheckForPInvokeThisCallWithNoArgs detects the invalid scenario
• Check is applied to both calli instructions and regular PInvoke calls
• Error message matches the existing check in the JIT compiler

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/coreclr/interpreter/compiler.h	Adds declaration for the new validation function
src/coreclr/interpreter/compiler.cpp	Implements the validation function and adds calls at two locations: for calli instructions and for direct PInvoke calls