[4.x] Update to Mix v6

[driesvints]

This updates our build pipeline to Laravel Mix v6. Also bumps several other dependencies. I'll send in a separate PR later on to update Vue to v3.

I needed to remove the copy call from the Laravel Mix file because it was failing for some reason. I also find it a bit out that a directory is created outside this repo. I guess this was for testing purposes?

Closes #1019

[tomirons]

@driesvints with the update to sql-formatter there are now whitespaces where they shouldn't be. You can fix this by setting the language on the formatter to mysql but I'm not sure how it would act with a postgres database.

Here is the new output:

select
  *
from
  ` database `.` table `
where
  ` database `.` table `.` column ` = 1
limit
  1

[tomirons]

I found the offending commit (sql-formatter-org/sql-formatter@4811f38#diff-58e2b0847926d0ac02995956be8168eb526bb08d921edada1bcbb4e209afce27). Not sure why they did that and I'm not sure what the proper work around should be.