Though we currently have the knowledge of where the `key` for an
attribute binding appears during parsing, we do not propagate this
information to the output AST. This means that once we produce the
template AST, we have no way of mapping a template position to the key
span alone. The best we can currently do is map back to the
`sourceSpan`. This presents problems downstream, specifically for the
language service, where we cannot provide correct information about a
position in a template because the AST is not granular enough.
PR Close#38898
ba3f4c26bb