Add QSortFilterProxyModel clear-filter benchmark

Use QBENCHMARK_ONCE rather than QBENCHMARK to avoid skewing the results:
when the QBENCHMARK block is repeated multiple times after the setup
code above runs once, only the first setFilterRegularExpression() call
unfilters some rows, while the subsequent calls simply check that there
is nothing to do.

The added benchmark is sensitive to the inefficiency - quadratic rather
than linear time complexity - fixed by
7d92ef63d7c2d9d017d89905a2ee0d1e9226b15c. The following two tables
contain the benchmark results on my GNU/Linux system. The numbers denote
milliseconds per iteration.

1. Qt 5.15.2 without the performance fix:
                    10K 25K 50K     100K    250K    500K
       no match     0    1    2       5       14       28
            all     0    0    0       1        3        7
          first     0    1    2       5       14       28
         1000th     2    6   12      25       68      302
         middle     3   34  132     518     3300    13665
1000th from end     1    4    9      19       50      103
           last     0    1    2       5       14       30
  each 10'000th     0   39  211     937     6326    41050
 each 100'000th     0    1    2       5     4226    34780

Without the fix the benchmark times out and aborts at 1000K and 2000K
data rows.

2. Qt 5.15.2 with the performance fix:
                    10K 25K 50K 100K    250K    500K    1000K   2000K
       no match     0   1   2   4       12      26       56      136
            all     0   0   0   1        3       7       14       28
          first     0   1   2   4       12      26       56      136
         1000th     0   1   2   4       13      28       62      145
         middle     0   1   2   4       13      27       59      142
1000th from end     0   1   2   4       13      28       60      145
           last     0   1   2   4       13      27       59      141
  each 10'000th     0   1   2   6       22      69      290     1413
 each 100'000th     0   1   2   4       13      30       81      261

Change-Id: I419a5521dd0be7676fbb09b34b4069d4a76423b1
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

0 files changed, 0 insertions, 0 deletions