Upgrade to laravel-mix v6 (webpack v5) and other js dependencies

Summary:

1. It makes the compilation 2 times faster for me
2. Most importantly, this is a bugfix for the vue-i18n related issue.

Test Plan: ./phpuint --testsuite=Browser

Reviewers: #hkccp_developers, mollekopf

Reviewed By: #hkccp_developers, mollekopf

Subscribers: mollekopf, #hkccp_developers

Differential Revision: https://git.kolab.org/D2401