FakeVim: Use QTextDocument::availableUndoSteps() for undo/redo
FakeVim: Use QTextDocument::availableUndoSteps() for undo/redo

Partially reverts commit b9cc16e405378a927cf013ef0b89c964532aa03a.

Using QTextDocument::revision() to keep track which undo/redo command
should be used next doesn't help much and it's more difficult to use
than QTextDocument::availableUndoSteps().

Task-number: QTCREATORBUG-9784
Change-Id: I656e1e964477de0f387c80b9384a32e0d8dab39f
Reviewed-by: hjk <f81b91af79013637d070c18d38a75b90eaae8ba3@nokiamail.com>

xianian/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,colede/qtcreator,xianian/qt-creator,omniacreator/qtcreator,colede/qtcreator,farseerri/git_code,richardmg/qtcreator,omniacreator/qtcreator,omniacreator/qtcreator,amyvmiwei/qt-creator,amyvmiwei/qt-creator,Distrotech/qtcreator,AltarBeastiful/qt-creator,kuba1/qtcreator,martyone/sailfish-qtcreator,richardmg/qtcreator,danimo/qt-creator,maui-packages/qt-creator,kuba1/qtcreator,farseerri/git_code,Distrotech/qtcreator,kuba1/qtcreator,xianian/qt-creator,danimo/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,danimo/qt-creator,Distrotech/qtcreator,colede/qtcreator,AltarBeastiful/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,colede/qtcreator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,kuba1/qtcreator,farseerri/git_code,darksylinc/qt-creator,AltarBeastiful/qt-creator,richardmg/qtcreator,omniacreator/qtcreator,xianian/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,farseerri/git_code,amyvmiwei/qt-creator,darksylinc/qt-creator,colede/qtcreator,farseerri/git_code,kuba1/qtcreator,richardmg/qtcreator,xianian/qt-creator,farseerri/git_code,maui-packages/qt-creator,danimo/qt-creator,omniacreator/qtcreator,colede/qtcreator,kuba1/qtcreator,darksylinc/qt-creator,farseerri/git_code,Distrotech/qtcreator,richardmg/qtcreator,Distrotech/qtcreator,maui-packages/qt-creator,AltarBeastiful/qt-creator,darksylinc/qt-creator,kuba1/qtcreator,xianian/qt-creator,omniacreator/qtcreator,maui-packages/qt-creator,AltarBeastiful/qt-creator,darksylinc/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,farseerri/git_code,darksylinc/qt-creator,martyone/sailfish-qtcreator,colede/qtcreator,xianian/qt-creator,Distrotech/qtcreator,danimo/qt-creator,darksylinc/qt-creator,maui-packages/qt-creator,amyvmiwei/qt-creator,amyvmiwei/qt-creator,AltarBeastiful/qt-creator,Distrotech/qtcreator,maui-packages/qt-creator,darksylinc/qt-creator,richardmg/qtcreator,amyvmiwei/qt-creator,amyvmiwei/qt-creator,richardmg/qtcreator,maui-packages/qt-creator,xianian/qt-creator,kuba1/qtcreator,martyone/sailfish-qtcreator,omniacreator/qtcreator