Summary:
Port QRegExp::exactMatch() by using QRegularExpression::anchoredPattern(),
unless the pattern is already anchored by "^" and "$".

BacktraceLineGdb::parse():
 - set QRegularExpression::DotMatchesEverythingOption, since gdb breaks
   some stack frame lines to mulitple lines for readability, e.g.:
   "#5  0x00007f50e99f776f in QWidget::testAttribute_helper (this=0x6e6440,\n
    attribute=Qt::WA_WState_Created) at kernel/qwidget.cpp:9081\n"
   this matches QRegExp behaviour where a "." char matches new lines by
   default.
 - Use clustering parentheses (?:) so as not to capture groups that aren't
   needed, less bookkeeping for QRegularExpression/PCRE

Replace QRegularExpression with QString comparison, the latter is usually
faster.

All unit tests still pass.

Reviewers: #plasma, davidedmundson, sitter, apol

Reviewed By: sitter

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28042