Redo doc strings for ERC's entry point commands

Redo doc strings for ERC's entry point commands

* lisp/erc/erc.el: Bump Compat version in Package-Requires header to
29.1.4.4.
(erc-select-read-args): Revise doc string, and update name of internal
`--interactive-env--' entry-point parameter.
(erc, erc-tls): Don't use `&interactive-env' as a variable name, in
case it confuses persons or programs.  Overhaul doc string in response
to user complaints.  For `erc' specifically, include literal
`:keyword' symbols to help non-Emacs users understand the required
syntax, which isn't obvious without an example, like `erc-tls' has,
and with only "&key" and upcased metasynctatic variables to go by.
(erc--current-buffer-joined-p): Remove assertion.
* test/lisp/erc/erc-scenarios-keep-place-indicator.el
(erc-scenarios-keep-place-indicator--follow): Try waiting for
intermittently failing condition.
* test/lisp/erc/erc-tests.el (erc-select-read-args): Update name of
internal keyword variable.