qt dependency: adapt to the qmake command changed name

Qt now has official guidance for the symlinked names of the tools, which
is great.

Qt now officially calls the tools `fooX` instead of `foo-qtX` where the
major version of Qt is X. Which is not great, because a bit of an
unofficial standard had prior art and now needs to change, and we never
adapted.

Prefer the official name whenever looking up qmake, and in the
testsuite, specifically look only for the official name on versions of
qt which we know should have that.

mesonbuild/dependencies/qt.py

@@ -245,7 +245,7 @@ class QmakeQtDependency(_QtBase, ConfigToolDependency, metaclass=abc.ABCMeta):
 
     def __init__(self, name: str, env: 'Environment', kwargs: T.Dict[str, T.Any]):
         _QtBase.__init__(self, name, kwargs)
-        self.tools = [f'qmake-{self.name}', 'qmake']
+        self.tools = [f'qmake{self.qtver}', f'qmake-{self.name}', 'qmake']
 
         # Add additional constraints that the Qt version is met, but preserve
         # any version requrements the user has set as well. For example, if Qt5

unittests/linuxliketests.py

@@ -387,8 +387,8 @@ class LinuxlikeTests(BasePlatformTests):
         Test that qt6 detection with qmake works. This can't be an ordinary
         test case because it involves setting the environment.
         '''
-        # Verify that qmake is for Qt5
-        if not shutil.which('qmake-qt6'):
+        # Verify that qmake is for Qt6
+        if not shutil.which('qmake6'):
             if not shutil.which('qmake'):
                 raise SkipTest('QMake not found')
             output = subprocess.getoutput('qmake --version')