Convert define-slot to Typescript (#25149)

* Convert define-slot to TypeScript

Co-authored-by: Jake Lee Kennedy <jlkennedy127@gmail.com>
Co-authored-by: Zeke Hunter-Green <zeke.huntergreen@guardian.co.uk>

* Convert define-slot to Typescript

Co-authored-by: Ravi Lal <arelra@users.noreply.github.com>
Co-authored-by: Dominik Lander <dominik.lander@guardian.co.uk>
Co-authored-by: Zeke Hunter-Green <zeke.huntergreen@guardian.co.uk>

* simplify and describe getSizeOpts

* unused export in Advert.ts

* better name for ias slot targeting

* improve function naming, docs and tests for define-slot

* use viewport sizes from source

* rebuild commercial bundle graph

* mock adSize in different test

* improve desc of collectSizes

Co-authored-by: Ravi Lal <arelra@users.noreply.github.com>
Co-authored-by: Zeke Hunter-Green <zeke.huntergreen@guardian.co.uk>
Co-authored-by: Dominik Lander <dominik.lander@guardian.co.uk>