IDL compiler: rename desc, proto, instance to *Template

More descriptive names:
desc => functionTemplate
instance => instanceTemplate
proto => prototypeTemplate

Largely:
sed -ri \
  '\, *//, ! s/\<proto\>/prototypeTemplate/' \
  $(git ls-files)
...to skip comments, though a few custom tweaks to code_generator_v8.pm
and to Python templates, due to block comments.

TBR=haraken

Review URL: https://codereview.chromium.org/68213020

git-svn-id: svn://svn.chromium.org/blink/trunk@162092 bbb929c8-8fbe-4397-9dbb-9b2b20218538