Cause shader recompilation when changing shader constants in GLES

[DerSchmale]

Description When using GLES as a backend, shaders would not recompile when changing push constants because they were not included in the program cache key. They are now, but the way the key field is generated could be improved.

Testing Using a simple shader choosing between two colours depending on an override constant.

Squash or Rebase?

Squash

[Wumpf]

resolved: title was misleading, this not about push constants which shouldn't be part of shader compilation, but rather about shader constants

[inner-daemons]

@DerSchmale Any updates on this?

[DerSchmale]

Hey not yet, I've been swamped with work and haven't had the time to properly fix this. My apologies for this.

[DerSchmale]

Force of habit, changed it to to_ne_bytes.

[inner-daemons]

@jimblandy This should be good to look at again soon, its just a few lines