The reserved-type-name binding diagnostic fired correctly but underlined the
enclosing statement / if / while / for / match / protocol / #objc_class block
because every binding-name check reused the parent `node.span`.
Thread each binding name's own span through the AST and parser, and pass it to
`checkBindingNames`:
- ast: add name spans to VarDecl, DestructureDecl, If/WhileExpr, ForExpr
(capture + index), MatchArm, Catch/OnFailStmt, Protocol/ForeignMethodDecl.
- parser: populate each span at the binding site from the name token's loc;
destructure reuses each target identifier's own span.
- semantic_diagnostics: every checkBindingName call now passes the binding's
own span — no site falls back to node.span. fn/lambda params already used
Param.name_span.
Carets now land on the offending identifier itself. New regression
examples/1125 asserts the protocol default-body and sx-defined #objc_class
method param spans; 0125/1119-1124 expected updated to the precise carets.
