BaseQtVersion: remove qmakeProperty(...) getter

Qt 6 will not use qmake to identify a Qt version, so this can not
be part of the public interface of BaseQtVersion anymore.

Provide getters for the information actually read via qmakeProperty(...).

Use the getters whenever possible.

Change-Id: Iadbee80b75e4f8b06caf90e7ed69fae2029b4dd7
Reviewed-by: hjk <hjk@qt.io>

src/plugins/android/androidbuildapkstep.cpp

@@ -212,7 +212,7 @@ bool AndroidBuildApkStep::init()
     if (!AbstractProcessStep::init())
         return false;
 
-    QString command = version->qmakeProperty("QT_HOST_BINS");
+    QString command = version->hostBinPath().toString();
     if (!command.endsWith('/'))
         command += '/';
     command += "androiddeployqt";