Add Ruby linter with Steep (#4671)

* Add Ruby linter with Steep

Fixes #3254

* Run steep instead of using language server

LSP presents a few issues and this works around those.

* Work around Steep path issue

See https://github.com/soutaro/steep/pull/975

* Add simple tests for steep

* Add steep to supported tools

* Pass linter

* Add a comment regarding Steep's column counting

* Make lnum an integer

* Add Steep handler test

* Fix separator for Windows

* Escape Windows path separators for substitute()

* Use ALEInfo (I) group

* Use fnameescape instead of quotes

* Skip linting for files not under steep root

* Add and pass tests covering proper steep root lookup

* Fix separator discrepancy

* Use strict operators (match case)

* Fix ordering

* Use `is#` instead of `==#`

doc/ale-supported-languages-and-tools.txt

@@ -572,6 +572,7 @@ Notes:
   * `solargraph`
   * `sorbet`
   * `standardrb`
+  * `steep`
   * `syntax_tree`
 * Rust
   * `cargo`!!