[TextLayer] Only cache the current `textDiv` style when `enhanceTextSelection` is enabled
[TextLayer] Only cache the current `textDiv` style when `enhanceTextSelection` is enabled

This will help save a little bit of memory, by not storing one unused string for each `textDiv` in regular text-selection mode.

macroplant/pdf.js,xavier114fch/pdf.js,mozilla/pdf.js,mozilla/pdf.js,Snuffleupagus/pdf.js,Shoobx/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,timvandermeij/pdf.js,timvandermeij/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,mainegreen/pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js,mainegreen/pdf.js,timvandermeij/pdf.js,Shoobx/pdf.js,xavier114fch/pdf.js,caremerge/pdf.js,showpad/mozilla-pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js,macroplant/pdf.js,caremerge/pdf.js