Fix #27319: Text editor "Find" does not locate words.

Fix #27319: Text editor "Find" does not locate words.

Added new option to find panel of space text which toggles
case-esensitive search.

Additional changes:
- Send NC_TEXT|NA_EDITED when removing markers in find_and_replace modifier
  this prevents "sticked" markers which disappears on first redraw when
  search text wasn't found
- Do not show "Text wasn't found" error when text to be searched is contained
  in the end of buffer and it's selected. Replacing/marking used to happen, but
  this popup message was really annoying for this case.

TODO: It's incorrect to use UI_GetThemeColor4ubv from this operator