Show the variable context in "go to symbol in editor/workspace"

[harrisont]

For example, TypeScript shows the container that the variable is in (the getReferences function is in the ReferenceProvider class):

Include the variable container as its context:

• A struct's variable's container is the struct name.
• A function's variable's container is the function name.

Implementation details

• Modify getDocumentSymbols/getWorkspaceSymbols to include the "children" symbols in the children field in the DocumentSymbols that it returns, and remove the "children" symbols from the top-level symbols (otherwise they'll be duplicated).