Create migration rule for bootstrap position helpers

[alizedebray]

We will soon introduce named z-index position classes.

As a result, Bootstrap's position helpers will no longer be necessary and can be replaced by a combination of other utility classes.

Goal

• Create a migration rule in our ESLint package that automatically replaces:
  • fixed-[top/bottom] with position-fixed [top/bottom]-0 start-0 end-0 z-fixed
  • sticky-[top/bottom] with position-sticky [top/bottom]-0 z-header
• Document the migration rule in the ESLint package
• Add tests for the rule
• Add information that we have an auto-migration in the migration guide
• Replace the classes in our own codebase

[oliverschuerch]

Question for the DEV Roundtable: Should we add this to the migration guide?

[gfellerph]

• Would be nice to have automigrations for these for projects
• Where would we draw the border of what's in scope?
• Can we scope migrations to utilities?
• Stick to past resolution (only prepare migrations if we documented it before)

Solution: offer automigrations for utilities and helpers where we have a fallback, but don't offer this for components or other parts of bootstrap (variables, functions, mixins, ...)

@leagrdv create tickets for remaining automigrations