Make a single 'PluginRegistry' and share it between SwiftASTManager,
IDEInspectionInstance, and CompileInstance. And inject the plugin
registry to ASTContext right after 'CompilerInstance.setup()'
That way, all sema-capable ASTContext in SourceKit share a single
PluginRegistry.
This hooks up the cursor info infrastructure to be able to pass through multiple, ambiguous results. There are still minor issues that cause solver-based cursor info to not actually report the ambiguous results but those will be fixed in a follow-up PR.
This allows us to model the `ResolvedCursorInfo` types as a proper type hierarchy instead of having to store all values in the base `ResolvedCursorInfo` type.
rdar://102853071
We need swiftsourcedocinfo for cursor info and to be able to reuse the ASTContext from code completion for cursor info, we need to also retrieve the sourcedocinfo for code completion requests.
