gn2bp: add basic parser support for copy and action_foreach rules

*Very* basic GnParser support for copy and action_foreach targets.
Copy rules are not very common, for cronet package only two are invoked:

- //components/cronet/android:cronet_package_copy_native_lib
- //third_party/icu:icudata

(I am using a heavily pruned version of cronet_package, it is possible
that the upstreamed version includes more such rules).

Test: parse //components/cronet:cronet_package
Change-Id: I47cd077b7f6261085d8006596df165f27a83a1d8
1 file changed