This refactors SelfApplyExpr.getFunction() as MethodLookupExpr().getMethodRef().
This is simpler, because we are not hiding DeclRefExprs or reinventing hidden AST resolution.
The test was inspired by locally running the query against files in
https://github.com/apple/swift/tree/main/test/Parse
A query for missing elements was also added to the AST tests, expecting
nothing to be found.
Also make `visit` in `SwiftDispatcher` work on `const` pointers.
Also, fixed a bug where the guard of a `CaseLabelItem` was not being
extracted, hence the test updates.
This fixes `IfConfigDecl` for both the AST printer and control flow
libraries.
It turns out that the active lements of an `IfConfigDecl` are already
listed in the enclosing scope (like a `BraceStmt`), so they should not
be listed as children, and `IfConfigDecl` can be jsut a leaf in the
control flow.
The `ParentChild` tests have been generalized to test all `PrintAst`
by factoring out `PrintAstNode` into a separate file.
The `child.ql` and `parent.ql` tests have been removed as they are
subsumed by `PrintAst.ql`. Also, a new `no_parent_child_loops` is
added to detect back edges to a root node (back edges to a non-root
node are already detected by `no_double_parents.ql`).
