For years, users have complained that the CodeMirror toggle button is
confusing and concealed. The icon looked too similar to the edit icon,
when it was supposed to be a highlighter. The new icon is similar but
has a highlighted line to help clarify what it is. We also now have the
text 'Syntax' accompanying the icon. Translators are instructed to try
to be brief to conserve space in the toolbar. "Syntax highlighting" is
the full correct term, and remains the text for the button's tooltip.
The new icon is ~0.3KB uncompressed, just meeting performance guidelines
for using @embed <https://w.wiki/AsPW>. This is also only temporary until the icon is upstreamed in Codex/OOUI.
New icon courtesy of Thiemo Kreuz (WMDE)
A corresponding change for the 2017 editor will follow I15453b33e7.
Bug: T174145
Change-Id: Ib6dbfc261214ed6672c1a54738e3401fa2f5d262
