1. Do not modify the map after loading. Instead, return string views
(guaranteed to be null-terminated) from look up functions and return
the key directly if not found.
2. Use an `unorded_map` instead of `map` where available (C++20).
Saves a bit of RAM (~50 KiB) and improves lookup performance.
We ensure that selectable lines are placed at the same vertical
coordinates but space out unselectable text lines at the cost
of reduced heigh of empty space between the store items.
We also have to move the back button in scrollable lists to the
lower right.
This can definitely be improved further but at least it solves
the problem for now.
Refs #3162
Gleb Mazovetskiy
Anders Jenbo
John Törnblom