Fix floating point <-> integer conversions

[janvorli]

This change uses JIT helpers to implement the floating point to integer and vice versa conversions.

[Copilot]

Pull Request Overview

This PR aims to fix and standardize the floating point to integer (and vice versa) conversion logic by leveraging JIT helper functions.

• Introduced new FCDECL helper calls for various conversion scenarios.
• Replaced traditional cast-based conversions with helper calls via HCCALL1.
• Implemented previously unhandled conversion cases (e.g., UINT conversions) by replacing assert(0) with helper calls.

Comments suppressed due to low confidence (3)

src/coreclr/vm/interpexec.cpp:250

• The conversion now employs HCCALL1(JIT_Dbl2Int, ...) for converting a float to int, replacing a direct cast. Please verify that the helper function preserves the intended conversion semantics compared to the previous implementation.

LOCAL_VAR(ip[1], int32_t) = (int8_t)HCCALL1(JIT_Dbl2Int, (double)LOCAL_VAR(ip[2], float));

src/coreclr/vm/interpexec.cpp:318

• Replacing the previous assert(0) with a helper call for INTOP_CONV_U4_R8 alters the behavior. Please ensure that JIT_Dbl2UInt correctly handles the conversion edge cases that were originally unimplemented.

LOCAL_VAR(ip[1], uint32_t) = HCCALL1(JIT_Dbl2UInt, LOCAL_VAR(ip[2], double));

src/coreclr/vm/interpexec.cpp:366

• Replacing the TODO and assert(0) in INTOP_CONV_U8_R8 with a helper call changes the conversion behavior. Confirm that JIT_Dbl2ULng implements the intended logic for converting a double to an unsigned long.

LOCAL_VAR(ip[1], uint64_t) = HCCALL1(JIT_Dbl2ULng, LOCAL_VAR(ip[2], double));

[janvorli]

/ba-g #116261