Both `try?` and `try!` are catch nodes, because they catch an error
thrown in their subexpression and handle it. Introduce an ASTScope for
all `try/try?/try1` expressions so we can find them, and model them as
catch nodes.
Fixes rdar://119216455.
Replace a number of virtual query functions like `getDeclIfAny`, which had
to be overridden at various points in the hierarchy, with simpler
implementations based on the scope kind and `dyn_cast`.
Macro-metaprogram whether each scope node is associated with a
particular declaration/statement/expression/attribute so these
implementations can be efficiently macro-metaprogrammed.
The ASTScope class hierarchy rooted at ASTScopeImpl is relying entirely
on overridden virtual functions and, in some cases, string comparisons
on the class name, to provide customization for the various classes.
Introduce proper LLVM dynamic casting support to this class hierarchy,
eliminating the string comparisons and the manually-specified
implementations of `getClassName` (which is now used only for printing).
We've been meaning to do this for years, but today I got angry enough.
