Add components to support skeleton loading states (#4052)

* adds skeleton components and stories

* supports use of skeletons in AvatarStack and AvatarPair

* replaces ad-hoc skeleton loaders in DataTable and TreeView

* adds VRTs

* rm unused stuff from stories

* adds component prop docs for Skeleton components

* adds changeset

* disable animations for VRTs and aXe tests

* fix typos in skeletonbone VRTs/AATs

* test(vrt): update snapshots

* adds skeleton loader example using React Suspense

* renames 'SkeletonBone' to 'SkeletonBox'

* updates needed since this PR was opened so long ago

* try resetting package-lock to whats in main

* appease the linter

* moves BaseSkeletonBox styles to SkeletonBox, and co-locates skeleton component specific styles to their components

* replace 'sx' prop with 'className' where possible

* rm sx usage, appease linter

* updates snaps, rms sx from story argtypes

* test(Skeleton): update id for SkeletonBox stories

* chore: update snapshots

* test(vrt): update snapshots

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Co-authored-by: mperrotti <[email protected]>
Co-authored-by: Josh Black <[email protected]>

Author: mperrotti