Due to using bold as a highlight style, the VE overlay technique
will only work with monospaced fonts.
Change-Id: I33e3e07cf0f3d8e25dd35623286eedf28ba20ae1
CM surface is just for presentation, it shouldn't
be possible to focus or select anything in the surface,
so in addition to it being beneath the VE surface,
disable it through the CM API and disable pointer-events
with CSS.
Bug: T170170
Change-Id: Ief49c293f514e22bc6db5eebb3a11c1bc695432d
Long-term todo:
* Performance will be poor on large pages due
to using a auto-height textarea which CodeMirror
doesn't optimise.
Change-Id: I16598fcdbeee51e6fae88376ec81f1c8552b383d