Constructing a constant SIMD::Float is not guaranteed to preserve the
data's exact bit pattern, but SPIR-V provides 32-bit words representing
"the bit pattern for the constant". Thus we must first construct an
integer constant, and bitcast to float.

Bug: b/140302841
Change-Id: I1a84dab9d1adbdc15f8a3b2fc639c637d2841174
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36208
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>