Add x64 disasm regression for BitConverter.SingleToInt32Bits in hot Span<float> loops

[Copilot]

BitConverter.SingleToInt32Bits in tight Span<float> loops can regress to a stack roundtrip (movss store + mov reload) instead of a direct register transfer (movd). This PR adds a focused JIT regression test to lock in the expected x64 codegen shape.

• Regression coverage

  • Adds src/tests/JIT/Regression/JitBlue/Runtime_130999/Runtime_130999.cs.
  • Exercises SingleToInt32Bits in a hot loop with an additional float use to keep the value in FP registers before bit reinterpretation.
  • Includes disasm assertions for x64 to require register-file transfer and reject stack-spill pattern.

• Disasm check wiring

  • Adds Runtime_130999.csproj with HasDisasmCheck=true and standard JIT test env settings for deterministic disasm validation.

• Functional guardrails

  • Verifies runtime behavior across empty, single-element, mixed, and edge-case float inputs (NaN, infinities, epsilon) so the codegen check remains attached to a correct computation path.

// X64-FULL-LINE: vmovd [[REG:[a-z0-9]+]], xmm{{[0-9]+}}
// X64-FULL-LINE-NEXT: add {{[a-z0-9]+}}, [[REG]]
// X64-NOT: movss dword ptr [rsp
acc += BitConverter.SingleToInt32Bits(f);