Since Core::Object properties are really only used by GML now that the
Inspector is long gone, there's no need for these to pollute
Core::Object.
This patch adds a new GUI::Object class to hold properties, and makes
it the new base class of GUI::Window, GUI::Widget and GUI::Layout.
The "instantiate an object by name" mechanism that GML uses is also
hoisted into GUI::Object as well.
If a widget gains a layout manager after it already has child widgets,
the existing widgets are unknown to the layout. Additionally, if a
layout is reused, it may end up managing children of multiple different
widgets.
To simplify this, clear the entries of a layout manager when its owner
changes, and add any existing children when a new owner comes along.
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 *
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
