add enum-tests into run-tests.rkt
Fix source locations for TR for.
Log sequence specialization failures in `for' loops.

Using this logging, Optimization Coach can recommend adding `in-list'
and co. to `for' loops in hot code.
Fix test for TR's for source locations.
Add more syntax examples to the reference
Fix tc-toplevel-form for ignored syntax
Make `require/typed` work at top-level

Closes PR 13747
Refactor to reduce right-ward drift
Whitespace and comment fixes
Reduce code duplication in Redex enum