In order for SwANGLE to expose GL_EXT_float_blend,
R32F, RG32F and RGBA32F must all allow blending.
The code already supports this, we just need to
expose the VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BLEND_BIT
bit for these formats.

Bug: b/146340613
Tests: dEQP-VK.pipeline.blend.*32_sfloat*
Change-Id: I39fc67fa8c26e8296f5e837a8b228a71df9149f1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39631
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>