IDL compiler: rename data_type => idl_type

In the CG we use |idl_type| for IDL types, to contrast with C++ types.
For consistency, use |idl_type| in parser as well.

This is just:
sed -i 's/data_type/idl_type/g' *.py

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/48013002

git-svn-id: svn://svn.chromium.org/blink/trunk@160695 bbb929c8-8fbe-4397-9dbb-9b2b20218538