editorconfig.el: Miscellaneous minor changes

editorconfig.el: Miscellaneous minor changes

* lisp/editorconfig.el: Drop redundant `require`s of pcase, nadvice, rx.
Remove unnecessary (and incorrect) `defvar`s in `eval-when-compile`.
(find-library-name, lm-version): Move declarations to right after
the corresponding `require` so we have a reason to believe they're defined.
(editorconfig-version): Use `package-get-version` when available.

* lisp/editorconfig-core.el (editorconfig-core-get-nearest-editorconfig)
(editorconfig-core-get-properties, editorconfig-core-get-properties-hash):
* lisp/editorconfig-fnmatch.el (editorconfig-fnmatch-p):
Remove autoload cookies.