* lisp/so-long.el: (so-long-statistics-excessive-p): New predicate
function using `buffer-line-statistics'.
(so-long-predicate): Use `so-long-statistics-excessive-p' by default.
* etc/NEWS: Describe changes.
* test/lisp/so-long-tests/so-long-tests-helpers.el:
* test/lisp/so-long-tests/so-long-tests.el: Update tests.
Also improve the existing `so-long-tests-predicate' tests.
The default values support preserving the state of `view-mode' when
switching to (and reverting from) `so-long-mode' (bug#45084).
* lisp/so-long.el (so-long-mode-preserved-variables)
(so-long-mode-preserved-minor-modes): New user options.
(so-long-mode-maintain-preserved-variables)
(so-long-mode-maintain-preserved-minor-modes): New functions.
(so-long-remember-all, so-long-after-change-major-mode)
(so-long-mode-revert): Use them.
* etc/NEWS: Describe changes.
* test/lisp/so-long-tests/so-long-tests-helpers.el:
* test/lisp/so-long-tests/so-long-tests.el: Update tests.
