When tab-bar-mode is on, (window-at 0 0) returns nil (because the
tab-bar is on that position), throwing off eldoc-box--window-side.
* eldoc-box.el (eldoc-box--window-side): Handle tab-bar differently.
* eldoc-box.el (eldoc-box--count-newlines): New function.
(eldoc-box--eldoc-message-function): Use eldoc-box--count-newlines to
count newlines.
(eldoc-box--enable)
(eldoc-box--disable): Use eldoc-display-functions instead of
eldoc-message-function when possible.
(eldoc-box--eldoc-display-function): New function.
* eldoc-box.el (eldoc-box--inhibit-childframe-timer): Remove
variable.
(eldoc-box--inhibit-childframe-for): Refactor to use
'run-with-idle-timer' instead of 'run-with-timer'
(eldoc-box--follow-cursor): Don't do anything if the timer is set
* eldoc-box.el (eldoc-box-eglot-help-at-point-last-point): Remove
variable.
(eldoc-box--eglot-help-at-point-cleanup): Remove function.
(eldoc-box-eglot-help-at-point): Use
'eldoc-box--help-at-point-cleanup' added in the last commit.
* eldoc-box.el (eldoc-box--help-at-point-last-point): New variable
(eldoc-box--help-at-point-cleanup): New function.
(eldoc-box-help-at-point): New command.
Quiet warnings from compiling, package-lint, checkdoc & byte-code compiling.
```
eldoc-box.el:264:2: Warning: docstring wider than 80 characters
227:4: warning: Closing parens should not be wrapped onto new lines.
eldoc-box.el:70: Keycode C-g embedded in doc string. Use \\<mapvar> & \\[command] instead
eldoc-box.el:145: Lisp symbol ‘self-insert-command’ should appear in quotes
eldoc-box.el:208: First line is not a complete sentence
eldoc-box.el:209: There should be two spaces after a period
eldoc-box.el:244: Argument ‘width’ should appear (as WIDTH) in the doc string
eldoc-box.el:265: Some lines are over 80 columns wide
eldoc-box.el:395: There should be two spaces after a period
eldoc-box.el:428: Keycode C-g embedded in doc string. Use \\<mapvar> & \\[command] instead
475:22: error: You should depend on (emacs "27.1") or the jsonrpc package if you need `jsonrpc-request'.
```
Prior to this change, single line eldoc messages were just ignored
completely when eldoc-box-only-multi-line was non-nil, though they
should have been displayed in the minibuffer.
* eldoc-box.el (eldoc-box--enable): Change :before-until to :before-while.
(eldoc-box--eldoc-message-function): Return nil if the message is not
multi-line, so that the default eldoc message function picks up the
message.
