Prepare mockito for the 'wildcard-variables' language feature.

[copybara-service]

Prepare mockito for the 'wildcard-variables' language feature.

We generally preserve positional parameter names, but in the case of wildcard
parameters, we must rename them. We cannot override a wildcard parameter with a
wildcard parameter, since we do use the parameter (we pass it to
super.noSuchMethod in a call to Invocation.method). This change introduces
some renaming logic for wildcard parameters, using new method-unique parameter
names.

[davidmorgan]

@srawlins thanks!

Looks like a similar fix is also needed for _buildOverridingSetter.