mem: rename align*Generic to align*

[motiejus]

Anecdote 1: The generic version is way more popular than the non-generic one in Zig codebase:

 git grep -w alignForward | wc -l
56
 git grep -w alignForwardGeneric | wc -l
149

 git grep -w alignBackward | wc -l
6
 git grep -w alignBackwardGeneric | wc -l
15

Anecdote 2: In my project (turbonss) that does much arithmetic and alignment I exclusively use the Generic functions.

Anecdote 3: we used only the Generic versions in the Macho Man's linker workshop.

[motiejus]

I'm happy to merge this - would you mind rebasing it?

Done. Also added @compileError(...) for the deprecated functions.