track-changes.el: Minor changes for version 1.0

track-changes.el: Minor changes for version 1.0

Arrange for the library to be usable on older Emacsen, which
includes reducing the noise when `before/after-change-functions`
are badly paired or missing.
Also, since the signal function receives the distance (for `:disjoint`),
we don't need `track-changes--disjoint-threshold`: the signal
function can simply do nothing when the distance is smaller than
the threshold it wants to use.

* lisp/emacs-lisp/track-changes.el: Prepare header for ELPA.
(track-changes--tracker, track-changes--state): Don't use `:noinline`,
so as to be compatible with Emacs<27.
(track-changes-record-errors): New variable.
(track-changes--recover-from-error): Use it.  Record only the last 20
keys and the last 50 stack frames in the error log.
(track-changes--disjoint-threshold): Delete variable.
(track-changes--before): Don't use it any more.

* lisp/progmodes/eglot.el (eglot--track-changes-signal):
Coalesce disjoint changes nearer than what used to be coalesced because of
`track-changes--disjoint-threshold`.