Store all enabled capabilities in the feature manger.

Store all enabled capabilities in the feature manger.

In order to keep track of all of the implicit capabilities as well as
the explicit ones, we will add them all to the feature manager.  That is
the object that needs to be queried when checking if a capability is
enabled.

The name of the "HasCapability" function in the module was changed to
make it more obvious that it does not check for implied capabilities.

Keep an spv_context and AssemblyGrammar in IRContext