Revert "Do NOT use exact match when updating dom selection"

The change to `exactMatch: false` in ianstormtaylor#4304
was intended to fix ianstormtaylor#4293,
a bug where "backwards typing" happened in nested editors.

But this change has introduced at least two new bugs:

- ianstormtaylor#4601
- ianstormtaylor#4626

These are (IMO) worse than the original "backwards typing" bug.

From discussion in ianstormtaylor#4304,
the true underlying bug is in ReactEditor.toSlateRange. I'll attempt to
fix this underlying bug instead.

packages/slate-react/src/components/editable.tsx

@@ -184,7 +184,7 @@ export const Editable = (props: EditableProps) => {
     // If the DOM selection is in the editor and the editor selection is already correct, we're done.
     if (hasDomSelection && hasDomSelectionInEditor && selection) {
       const slateRange = ReactEditor.toSlateRange(editor, domSelection, {
-        exactMatch: false,
+        exactMatch: true,
 
         // domSelection is not necessarily a valid Slate range
         // (e.g. when clicking on contentEditable:false element)