Simplify literal creation in SPIR-V.

We had several ways of creating one, zero, true, false, and arbitrary
literals throughout the code. These have all been simplified to
`writeLiteral(double, Type)`.

Change-Id: I8094f142d24b5068e1baf7db8a6148a22e864682
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/471377
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed