The previous version of this query inadvertently excluded constants
which weren't classes or modules. This version includes them, by
introducing a laxer version of `resolveScopeExpr` that doesn't require
the result to be a `TResolved`.
By convention, instance variables are considered to be "defined" in the
`#initialize` method of their containing class. If an instance variable
is written to in `#initialize` and then read elsewhere in the program,
we will point from the read to the write. If it is not written to in
`#initialize` then we won't provide any jump-to-definition information
for it.
We synthesise variables for things like tuple patterns. For example,
this Ruby code:
a, b = ...
becomes:
__synth__0 = ...
a = __synth__0[0]
b = __synth__0[1]
The `__synth__` variables should be ignored when calculating
jump-to-definition information, since they don't appear in the original
source code.
The expected output format is a tuple (a, b, k) where `a` and `b` are any
`AstNode` subclass and `k` is a string indicating the kind of
definition (e.g. variable, method, ...).
By ensuring that every value in `DefLoc` is a subclass of `Expr` (itself
a subclass of `AstNode`) we can simplify the query by removing all the
use of `getLocation()`.
