[jit] More float32 fixes. (#8234)
* [jit] Add a r8->r4 conversion in stind.r4 when the item on the stack is a r8 because of stack merging.
* [jit] Disable a SIMD test which can fail with -O=float32 due to precision problems.
* [jit] Use m_class_get_byval_arg ().
* [jit] Fix OP_RCONV_TO_I on amd64.
* [jit] Revert '[jit] Use r8 for r4 stack vars to avoid problems with stack merges when one side is an r4 and the other an r8. Add conversions for compares. (#8196)'. It causes r4-r4 merges to produce an r8 stack value, leading to invalid il errors.