Mojo C++ bindings: replace '::' with '.' in the interface name.

Previously the |foo::Bar::Name_| field was "foo::Bar". With this change it
becomes "foo.Bar".

Using C++-style namespace in the name doesn't makes too much sense because the
name should remain the same across different languages.

BUG=None

Review URL: https://codereview.chromium.org/1778793004

Cr-Commit-Position: refs/heads/master@{#380301}
6 files changed