Clarify docs for `collection-path'.

After discussion with Robby.
Fix PR 14140
Initialize base-special-env in TR typecheck tests
Add `in-set` to Typed Racket

Closes PR 14128
Adding test case for PR14136 re: the great Robby
Be more picky about Opaque type parsing

Closes PR 14122
add some corner cases in for.rktl tests
Fix gc2/gc1 inconsistency
Fix PR14142 by allowing 'tolerant' line endings acording to Appendix B of the HTTP spec
Get more info to diagnose intermittent failure on DrDr.
fix documentation typos
split up slideshow/play so that the pict-only parts are
in pict-lib and don't depend on racket/gui/base
add "File|Open Collection Path" to DrRacket

This menu item is an attempt to make it easier
to find collection-path based files for editing

Inspired by Asumu's raco-find-collection package
distro-build/package-and-catalog: extra options for checksums & paths
racket/gui cocoa: make 'border handling more flexible

When buttons are hidden and/or disabled so that there's a change to
the only button that is visible, enabled, and has the 'border style,
then make it the default.
guard against collection path directories that don't exist
adjust the sierpinski carpet examples to be bitmaps

This saves about 10 megs (from 16 or 6 ish) in the space
taken for the teachapack guide docs and seems to make the
guide page load a bunch faster
make new file|open variant start you out in the module path
where the file currently being edited lives
Name and print top types consistently

Closes PR 14117
Closes PR 14118
Revert type key change from 0a6537a6cbed7ca477d153

Sets are still treated as hash sets. Eventually
when we have a type for generic sets, it should have
a #f type key.