Avoid breaking kerning with continuous spell checking

Avoid breaking kerning with continuous spell checking

There is a mismatch between the way text is tokenized in Row objects
and the way it is shown on screen. When metrics are computed,
continuous spell checking has not been done yet. Yet, the row painter
explicitly breaks words at spell status boundaries. This creates
problem with a text like "PMP," (see bug #9649), where there is a
negative kerning before the comma.

This is solved by not taking in account spell status when drawing
text, and drawing spell underlines separately.

* replace Paragraph::isSameSpellRange with new method getSpellRange.

* merge RowPainter::paintChars into RowPainter::paintFromPos

* move the actual text painting code into the new paintTextAndSel.

* merge some code from paintFromPos to paintMisspelledMark

* in paintMisspelledMark, scan the string which needs to be annotated
  and add dashed line below text marked as misspelled.

Fixes bug #9649.