ToolButton has no redeeming differences with Button;
it's just a Button with the Flat property enabled by default.
Removing it avoids some confusion when creating GUIs.
Existing ToolButtons will be converted to Buttons, but the Flat
property won't be enabled automatically.
This closes https://github.com/godotengine/godot-proposals/issues/1081.
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.
Happy new year to the wonderful Godot community!
We're starting a new decade with a well-established, non-profit, free
and open source game engine, and tons of further improvements in the
pipeline from hundreds of contributors.
Godot will keep getting better, and we're looking forward to all the
games that the community will keep developing and releasing with it.
