There are SwiftShader related failures related to enabling the
textureCompressionASTCHDRKHR feature without properly checking if the
VK_EXT_texture_compression_astc_hdr extension is available, so HDR support
shouldn't be enabled only based on the LDR support being enabled.

Bug: angleproject:4447
Change-Id: Icde34892c9e2efff4b71e8c4e960c2fcff786700
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2080594
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>