Vendor selectionhighlight, bracketmatch, colorpreview, navigate, editorconfig (2.1.8-7)

Five more plugins from lite-xl-plugins @ 31eef29, all default VSCode
behaviors:

- selectionhighlight: highlights other occurrences of the selected word
- bracketmatch: highlights the bracket matching the one under the cursor
- colorpreview: inline swatches for #hex/rgb()/hsl() color literals
- navigate: Go Back / Go Forward cursor history (alt+left/right)
- editorconfig: applies .editorconfig files; vendored as the whole
  upstream directory (parser + test harness, lite-xl test editorconfig);
  builds on the bundled trimwhitespace plugin

All depend on core only (editorconfig additionally on trimwhitespace,
already shipped). Verified against the built package: all plugins load,
navigate registers its commands, and an .editorconfig with
indent_size = 2 is applied to an opened file.

Pinned to lite-xl-plugins @ 31eef29 (see debian/extra/README.source).

debian/extra/plugins/editorconfig/tests/parser/comments_only.in

@@ -0,0 +1 @@
+# Just a comment, nothing else