Support require/typed clauses in require/typed/provide

Closes PR 13901
Fix reading of config.rktd file when in strange readtable.
Examples for #:opaque and require/typed/provide
Move json tests to racket-test pkg.
Don't run special sandbox tests when the relevant libs are not available.
Create `unstable-debug-lib`, `unstable-pretty-lib`, `unstable-flonum-lib` packages.
Add `scribble-text-lib` package.
Add more correct dependencies for `racket-test`.
Fix unneeded R6RS dependency.
Disable broken contract test.
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some 2htdp/image equality clarification
adjust rotation discussion to use a circle, not a rectangle
adjust the pkg/main.rkt exports to be of the form
pkt-<X>-command to avoid conflicting with pkg/lib
adjust test to still test for <collects>/ prefix
by forging a source location in the collections
directories.

Thanks, Carl!
correct typo
separate htdp package into htdp-lib htdp-doc and an htdp package
that just pulls those two in: just the git mv commit
adjust info.rkt files for new htdp-doc pkg
fix contract
add image interop section to 2htdp/image