Implement initial support for `A.(B)` syntax, per #989. Specifically, this supports:
* `object.(Type.member)` for instance members,
* `object.(Interface.member)` for instance and non-instance members,
* `object.(Type.(Interface.member))` for instance members,
* `Type.(Interface.member)` for non-instance members.
Three new AST nodes are introduced:
* `CompoundFieldAccessExpression` represents the `A.(B)` syntax.
* `MemberName` is a `Value` that represents the result of evaluating an expression such as `Type.member` or `Interface.member` or `Type.(Interface.member)`.
* `TypeOfMemberName` is the type of a `MemberName` value.
In order to handle members of classes and interfaces which have corresponding declarations and may need substitution into their types, and members of structs which don't have declarations but also don't need substitution, a class `Member` is introduced that can refer to either of these kinds of member.
Co-authored-by: Geoff Romer <gromer@google.com>
Co-authored-by: Jon Meow <jperkins@google.com>
Use FileCheck's `[[@LINE+n]]` mechanism to refer to the next line.
This is made awkward by a couple of things:
* We want to keep the `CHECK` lines in the original order.
* Errors are sometimes more than one line long.
The approach we use is to interleave the original lines and the check lines, putting each check line as early as possible subject to two rules:
1) Check lines never precede the 'AUTOUPDATE' line
2) Except when required by rule (1), a check line that refers to a source line by line number is never placed earlier than a source line that precedes that source line.
The actual `[[@LINE+n]]` annotations are created in a second pass after we've interleaved the lines so that we can work out the correct offsets.
Co-authored-by: Jon Meow <jperkins@google.com>
