This change makes scrolling noticeably smoother on files with many
single-char text divs, such as the one in #1045. The trade-off is that
the visual appearance of text selection in such documents is slightly
worse, because more text divs overlap.
This change also uses `scaleX(N)` instead of `scale(N, 1)`. This might
be marginally more efficient in terms of JS string concatenation.
transformOrigin is set to 0% 0% in all cases. This adds extra memory
impact into the dom tree. It also involves the CustomStyles workaround
to determine the correct css rule for the browser.
By setting all vendor and standard variants in css, the rule is applied
without the dom memory overhead and without the minor computation
overhead to set the value.
The data-font-name attribute of textLayer divs are only used by the Font
Inspector. This change ensures they are only present when the pdfBug
tools are enabled.
This change improves the text layer creation of "normal" text heavy documents.
It changes 2 things:
* If the text element is not rotated, it will neither calculate nor apply a
textTransform: rotate(0deg) to the text layer element.
* For scaling the text layer div, the context will measure the width of the
text in the given font. For many text documents the font changes seldom.
If the font stays the same, the context does not need to be set to a new font
especially avoiding the temporary creation of the same font string over and
over again.
