Refactor compute_dependencies.py to use interfaces_info internally

This is a preliminary refactoring:
in the next CL I'll add [ImplementedAs] to the pickled interfaces_info,
(and then we can use it in the Python IDL compiler, which is the goal!),
but first I'm refactoring compute_dependencies.py to use interfaces_info
internally, rather than the current mess of multiple dictionaries and sets
for this information.

That is, compute_dependencies.py now has a single dictionary, keyed
by interface name, with all the global data for interfaces.
Previously there were 5 dictionaries or sets which had to cross-reference
each other, yielding a redundant mess, and very long function signatures.

It also cleans up various accumulated cruft.
(I've only cleaned up the cruft that's directly relevant to interfaces_info.)

Other than changing InterfacesInfo.pickle to contain a general-purpose
dictionary (not just a list of dependencies), the only change in output
is removing a trailing space from each line of the file of inputs to
bindings_derived_sources (cleanup).

Review URL: https://codereview.chromium.org/125163003

git-svn-id: svn://svn.chromium.org/blink/trunk@164664 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rename EventContext to NodeEventContext.

This is a follow-up patch for https://codereview.chromium.org/108723007/.

BUG=329445

Review URL: https://codereview.chromium.org/125593005

git-svn-id: svn://svn.chromium.org/blink/trunk@164665 bbb929c8-8fbe-4397-9dbb-9b2b20218538