Enforce preference of preincrementation wherever applicable

[Chubercik]

Although the performance boost might be negligible (if at all present due to how modern compilers should be able to squeeze out any optimizations possible), wouldn't it make sense to enforce a code quality check for using preincrementation in certain code structures, e.g. for loops, where we don't really care about the return value of the i++ statement?

As it stands, currently there are both i++ and ++i statements in Godot's codebase, enforcing one or the other would make it more uniform.

[Calinou]

Please check whether this is the case with Godbolt when using a modern GCC or Clang version with release optimizations enabled.

[Chubercik]

Fair enough, no difference in the resulting binary; what about code style unification?

[Calinou]

i++ should likely be preferred in this case as it's more commonly used overall, and maps more closely to i += 1 which is used elsewhere (and in GDScript).