Add `push`, `push_back`, `pop` & `pop_back` methods to fixed-size arrays

[alonely0]

Append/Push syntax for arrays versus dedicated methods versus ops::{Add, Sub}

This post tries to merge the recent discussion about push, append & pop (later on truncate) methods for arrays and the late-2020 to early-2021 discussion about push & append being language syntax. My point is to discuss whether to wait for better const expressions and get those methods into core, create an expansion syntax that does not collide with the range syntax, or overloading arithmetic operators. For the syntax, my proposals are: [...array, element1, element2], with chaining [...array…