* only include the given symbol for qualified imports
rdar://96309088
* re-exporting one type should not allow unrelated types to sneak in
* ensure that children of re-exported types are also re-exported
When emitting a symbol graph file for a module that import modules via
`@_exported import`, emits those modules' symbols as well.
SR-15753
rdar://89547374
When extending another module's type in your module, serialize declarations in
the extension into the other module's "extension" symbol graph file, including
relationships. This mechanic should continue up to the rootmost module. For
example:
A.AStruct <- B.BStruct < C.CStruct
Both BStruct and CStruct should go in `@A` symbol graph files because AStruct
owns BStruct and by extension owns CStruct. This is reflected in
documentation curation in some form already.
rdar://60796811
