Make base imports explicit.

mesonbuild/dependencies/__init__.py

@@ -12,7 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .base import *
+from .base import (  # noqa: F401
+    Dependency, DependencyException, DependencyMethods, ExternalProgram, ExternalLibrary, ExtraFrameworkDependency,
+    InternalDependency, PkgConfigDependency, find_external_dependency, get_dep_identifier, packages)
 from .dev import GMockDependency, GTestDependency, LLVMDependency, ValgrindDependency
 from .misc import BoostDependency, Python3Dependency, ThreadDependency
 from .platform import AppleFrameworks