Sort JavaScript imports in the CE code
to match our future ESLint configuration.

Part of our prettier migration; changing the arrow-parens style.

This removes $.fn.glDropdown and replaces it with the function
initDeprecatedJQueryDropdown. This ensures that modules which rely
on this function are not dependent on a globally accessible function
and also prevents naming confusion with the gitlab-ui component
also named GlDropdown.

Fix all JS files

This fixes all disabled lints for the `prefer-template` rule:
https://eslint.org/docs/rules/prefer-template

This fixes all disabled lints for the `prefer-arrow-callback` rule:
https://eslint.org/docs/rules/prefer-arrow-callback

This fixes all disabled lints for the `object-shorthand` rule:
https://eslint.org/docs/rules/object-shorthand

Update explicit headers to new format

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

This commit only targets Vanilla JS files.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

This commit only targets Vanilla JS files.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Squashed commit of the following:
    fix overlooked window binding in spec files
    remove imports loader
    replace implicit this == window with explicit binding