Fix an unreported issue with WMS client ignoring the advertised tile
size from GetCapabilities (because the raster iterator always used
its own hardcoded default).
A new method was added to retrieve this information from data providers
only implemented for WMS at the moment.
The test has been reformatted for consistency with other core tests
by moving the implementation outside of the class. The actual change is
the addition of TestQgsWmsProvider::testMaxTileSize().
Funded by: M.O.S.S. Computer Grafik Systeme GmbH https://www.moss.de/
2078ef5c03