compiler: Mangle generated method names that conflict with java.lang.Object methods

[shivaspeaks]

Generated gRPC method names in the BlockingV2Stub can conflict with
final methods on java.lang.Object (e.g., toString(), hashCode())
for client-streaming and bidi-streaming RPCs. This occurs because
they are generated with no arguments, leading to a compilation error. One such case in #12331.

This change introduces a dedicated list of no-argument method names
from java.lang.Object and applies name-mangling (appending an
underscore) only when generating these specific methods in the
v2 blocking stub.

This resolves the compilation failure while ensuring that the behavior
for all other stubs remains unchanged.

Fixes: #12331

[ejona86]

We should have this be a separate list. The current list is keywords. This new list should be limited to "methods on Object that have void arguments."