[clr-interp] Fix implicit promotion of I4 to I

[davidwrighton]

Ryujit does implicit promotion using zero-extending promotions for some opcode and sign extending for others. I don't see a particularly good rhyme or reason for the current behavior, but it does not match what the interpreter does.

This PR adds a test for all the opcodes that experience promotion, and attempts to test all the behaviors correctly. In building it, several issues were found/fixed.

This is known to fix the GitHub13501 test. in addition to the various issues found during test development.

[Copilot]

Pull request overview

This PR fixes implicit promotion of I4 (int32) to I (native int) in the CoreCLR interpreter to match RyuJIT's behavior. The fix addresses inconsistencies where some opcodes use zero-extension and others use sign-extension when promoting 32-bit integers to native integers on 64-bit platforms.

• Adds a new helper function to determine the correct widening operation (sign or zero extension) based on the opcode
• Implements comprehensive tests for all opcodes that perform implicit promotion, covering arithmetic, comparison, and branch operations
• Tests verify correct behavior for unsigned overflow operations (add.ovf.un, sub.ovf.un, mul.ovf.un) and unsigned branch/comparison operations (bne.un, blt.un, etc.)

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/coreclr/interpreter/compiler.cpp	Adds InterpOpForWideningArgForImplicitUpcast() to select appropriate conversion (sign vs zero extension) and updates EmitTwoArgBranch() and EmitBinaryArithmeticOp() to use it
src/tests/JIT/Methodical/int64/unsigned/implicit_promotion_il.il	New IL assembly defining 52 operator methods testing all promotion scenarios with mixed I4/I8 operands
src/tests/JIT/Methodical/int64/unsigned/implicit_promotion_il.ilproj	Project file for the IL test
src/tests/JIT/Methodical/int64/unsigned/implicit_promotion.cs	New C# test invoking IL operators with negative values to validate sign/zero extension behavior on 32-bit vs 64-bit platforms
src/tests/JIT/Methodical/Methodical_*.csproj	Updates to include the new test files in various build configurations

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[janvorli]

LGTM modulo the copilot nits that seem to make sense.