We hold a raw pointer to the mouse selection target, which is a mixin-
style class inherited only by JS::Cell classes. By not visiting this
object, we sometime had a dangling reference to it after it had been
garbage collected.
Previously, the`HTMLInputElement.selectinStart` and
`HTMLInputElement.selectionEnd` IDL setters, and the
`setRangeText()` IDL method were used when updating an input's value
on keyboard input. These methods can't be used for this purpose,
since selection doesn't apply to email type inputs. Therefore, this
change introduces internal-use only methods that don't check whether
selection applies to the given input.
The DOM spec defines what it means for an element to be an "editing
host", and the Editing spec does the same for the "editable" concept.
Replace our `Node::is_editable()` implementation with these
spec-compliant algorithms.
An editing host is an element that has the properties to make its
contents effectively editable. Editable elements are descendants of an
editing host. Concepts like the inheritable contenteditable attribute
are propagated through the editable algorithm.
Before this change, skipping a word to the left in a non empty text
input element would crash when near the end of the text as the
offset + length of the substring would exceed the length of the string.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
