examples/: compile with QT_NO_CONTEXTLESS_CONNECT

Examples are usually a good way to get to know a new codebase, do not
teach developers who are new to Qt about the 3-arg connect() to begin
with.

Drive-by changes:
- `this` can't be implicitly captured with [=] in a lambda, instead
  capture by reference
- Update docs related to the sqlbrowser example; the overloaded signal
  it mentions has been removed in Qt6
- In the sqlbrowser example, rename addConnection() (no-arg) overload to
  openNewConnectionDialog, suggested in code review

Change-Id: I30c9f35bda4ac2f460d767ab7f84422ae3ed09f7
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

0 files changed, 0 insertions, 0 deletions