Split out macros from interface.cpp.

method_configuration and install_custom_signature are moved to methods.cpp,
attribute_configuration is moved to attributes.cpp, and
constants is moved to newly created constants.cpp.

BUG=358074
TEST=no new tests, because of just refactoring.

Review URL: https://codereview.chromium.org/499373003

git-svn-id: svn://svn.chromium.org/blink/trunk@181088 bbb929c8-8fbe-4397-9dbb-9b2b20218538