problem view: faster implementation of resizeColumnsToContents

For large documents with lots of problems, switching the file
has a noticeable delay, caused by computing lots of size hints.
We can avoid that by using a heuristics instead.
1 job for !132 with faster-problem-view in 42 minutes and 47 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #47575
linux kf5-qt5 qt5.12

00:42:47

47.0%