Finding a better way to readjust the width of cloned textarea

Bug #1382890

Old fix involved a hard-coded font size which was bad
This involves finding the computed size in px of what all the
font-family/font-size/width etc that would have been in play and
giving the cloned textarea the same width.

Change-Id: Ia116d5474482b57d3a478adba14b304845253ebb
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Finding a better way to readjust the width of cloned textarea" into 1.10_STABLE