Bug 1939220 - part 3: Make TextFragmentData::BoundaryData not depend on the editing host r=m_kato

Its role is scanning the DOM.  Therefore, it can know which node is an editing
host during a scan.  Therefore, it does not require the editing host parameter.
To fix that, some utility methods of `HTMLEditUtils` needs to work with
non-editable nodes.  Therefore, this patch also updates `HTMLEditUtils`.

Finally, this gets rid of the `NS_ASSERTION`s in the constructor of
`TextFragmentData` because it'll be available with non-editable nodes too.
Although current all callers assume that it works as in an editing host.

Differential Revision: https://phabricator.services.mozilla.com/D232934

editor/libeditor/HTMLEditor.cpp

@@ -1181,7 +1181,7 @@ nsresult HTMLEditor::MaybeCollapseSelectionAtFirstEditableNode(
         // Chromium collapses selection to start of the editing host when this
         // is the last leaf content.  So, we don't need special handling here.
         leafContent = HTMLEditUtils::GetNextLeafContentOrNextBlockElement(
-            *leafElement, *editingHost,
+            *leafElement,
             {LeafNodeType::LeafNodeOrNonEditableNode,
              LeafNodeType::LeafNodeOrChildBlock},
             BlockInlineCheck::UseComputedDisplayStyle, editingHost);
@@ -1207,7 +1207,7 @@ nsresult HTMLEditor::MaybeCollapseSelectionAtFirstEditableNode(
       }
       // If it's an invisible text node, keep scanning next leaf.
       leafContent = HTMLEditUtils::GetNextLeafContentOrNextBlockElement(
-          *leafContent, *editingHost,
+          *leafContent,
           {LeafNodeType::LeafNodeOrNonEditableNode,
            LeafNodeType::LeafNodeOrChildBlock},
           BlockInlineCheck::UseComputedDisplayStyle, editingHost);
@@ -1254,7 +1254,7 @@ nsresult HTMLEditor::MaybeCollapseSelectionAtFirstEditableNode(
     // Otherwise, we must meet an empty block element or a data node like
     // comment node.  Let's ignore it.
     leafContent = HTMLEditUtils::GetNextLeafContentOrNextBlockElement(
-        *leafContent, *editingHost,
+        *leafContent,
         {LeafNodeType::LeafNodeOrNonEditableNode,
          LeafNodeType::LeafNodeOrChildBlock},
         BlockInlineCheck::UseComputedDisplayStyle, editingHost);