This patch adds a visibility state to GUI::Action. All actions default
to being visible. When invisible, they do not show up in toolbars on
menus (and importantly, they don't occupy any space).
This can be used to hide/show context-sensitive actions dynamically
without rebuilding menus and toolbars.
Thanks to Tim Slater for assuming that action visibility was a thing,
which gave me a reason to implement it! :^)
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
