Move the "Replace" popup option to the Text Selection ActionMode.

As a first step in unifying the cut/copy/paste ActionMode in Editor
with the paste/replace popup, I'm moving the replace option to
the CAB ActionMode. Paste is already there, so for now all options
are together.

Missing things to address in upcoming CLs:
- Invoke the ActionMode in all cases where the popup shows up now,
ensuring only the options that are currently available show up.
- Get rid of the current popup
- Make the ActionMode a floating toolbar (pending feature completion)
- Define a keyboard shortcut for replace?

Note that since the ActionMode still shows up in the ActionBar and
replace has no icon it now appears as text and takes up lots of
space. This will improve when we can switch to using a floating
toolbar.

Change-Id: Ib6b60bae9b58e4db96b9c4cee556e19d3f1bb466