Various improvements - Githubissues

[x] ~Black decided to change~ rebased.
[x] Can now assign to arrays.
[x] Constant vecs and constant data for arrays is actually represented as a SpirV constant.
[x] Composing a vector our of another (shorter) vector + more is more efficient.
[x] In more cases, avoid the use of variables when simple SSA will do.
[x] Fix a specific case where breaking out of a loop would ... break (pun intended).
[x] Fix handling of EXTENDED_ARG, so that control flow actually keeps working for longer shaders.
[x] Update the test hashes (many of the above changes cause changes in many of the hashes, which is why I decided to bundle it in one PR).

pygfx / pyshader