* source-mapping/source-map.el (source-map-read): Bind more edebug
variables before calling edebug-read-storing-offsets.

* source-mapping/source-map-bytecomp.el: Add TODOs. Add
backward-compatibility with Emacs 26+. Remove unused lexical variables.
More inline documentation. Removed source-map-aux-expression. Removed
source-map-expression constants since they should always be unique.
(source-map--ify): New function. Takes anything and returns a
source-map-expression of it. Works recursively on vectors and conses,
and any elements which are source-map-expressions are left as is, and
everything else is wrapped.
(source-map-bytecomp-annotated-lap): New function. Takes a symbol with a
bytecode-source-map property and returns an alist associating original
source code strings to LAP.