Make nsHTMLCopyEncoder::RangeNodeContext::IncludeInContext not treat inline editing host as an contextual inline element
It treats some inline elements as contextual elements. Then, they will be
preserved in copied HTML fragment. However, if an inline element is an editing
host, we don't want to contain it to the copied fragment because pasting it
causes duplicating same style into same editing host. So, if the style includes
relative style like font-size: 2em, it will cause bigger text than the
surrounding text. Additionally, the inline editing host usually has a border
but we don't want to make it appear in editable text.
Unfortunately, with this change, we stop copying the text style specified to
the inline editing host. However, this is same behavior as when the editing
host is a block element like <div>. Note that pasted text will be merged into
the inline editing host style. Therefore, if and only if the destination has
different style from the editing host, the result might be different from the
expected one by the user. However, this is a long standing issue, see
bug 1428046, for example.
Differential Revision: https://phabricator.services.mozilla.com/D228623
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1930277
gecko-commit: 060a278ac9c9372f565183bbb337b03ffdff3d7e
gecko-reviewers: edgar, dom-core