When creating a window, Godot would first register it to the WM(show it) and then set its flags.
This works fine on a floating WM, but on tiling WMs as soon as a window gets registered
the WM immediately acts on the window by scaling it up and treating it as a generic window,
being registered without any special flags.
This commit separates the showing of the window into another function and calls it after the most important flags are set,
making windows with special flags(eg. all popups) work again on tiling WMs.
Fixes#37930
Which means that reduz' beloved style which we all became used to
will now be changed automatically to remove the first empty line.
This makes us lean closer to 1TBS (the one true brace style) instead
of hybridating it with some Allman-inspired spacing.
There's still the case of braces around single-statement blocks that
needs to be addressed (but clang-format can't help with that, but
clang-tidy may if we agree about it).
Part of #33027.
It changed name as part of the DisplayServer and input refactoring
in #37317, with the rationale that input no longer goes through the
main loop, so the previous Input singleton now only does filtering.
But the gains in consistency are quite limited in the renaming, and
it breaks compatibility for all scripts and tutorials that access
the Input singleton via the scripting language. A temporary option
was suggested to keep the scripting singleton named `Input` even if
its type is `InputFilter`, but that adds inconsistency and breaks C#.
Fixesgodotengine/godot-proposals#639.
Fixes#37319.
Fixes#37690.
