Port remaining uses of QRegExp in src/vimode into QRegularExpression

Jan Paul Batrinarequested to merge
jbatrina/ktexteditor:qregexp-to-qregularexpression into master

The Changes were mostly QRegExp::[last]indexIn -> QString::[last]indexOf.

I have only done light testing (+the autotests) and so far I haven't found any regressions.

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