tweak bitwise-operation optimization

Recognize arguments that are variables bound to fixnums.
meta/new-web: gzip ".css" and ".js" on upload to S3

We assume that any web browser where ".css" or ".js" useful
can also handle gzipped content. Compress files that are
at least 1k.

Also, use the new "shallow" mode of s3-sync to speed updates
to download.racket-lang.org.
Adjust fixed mode and add new stlc counterexamples
add Michał Pałka's l
Fix description of citet requirements.
remove links synthesized information from drracket bug report
renumber poly-stlc bugs to start from 1
Misc cleanups to stlc and stlc-sub benchmarks:

 - add +
 - tweak definition of c to make more like Palka's dissertation
 - remove non-bugs from stlc-sub
 - share test suite between stlc and stlc-sub
Make TR class tests run successfully on their own

Closes PR 14409
add new stlc-sub bugs
unbreak stlc-sub test #9
redex: add virtual machine model to benchmark
change stlc-sub's 'check' function to not assume
its input is well-typed
add missing value production

also, use redex-check? instead of redex-check in 2 places
fix subst function

- its contract said it accepted M's as the third argument, but it
  worked only for v's
- remove two redundant cases
new slate of stlc-sub bugs
redex: fix rvm ordered generation in n benchmark
adjust enum distributions
redex: update virtual machine benchmark diffs
Handle init/init-field order correctly in TR

Also handles the case where init and init-field clauses
are interleaved, in which case they need to be interleaved
in the type.

Closes PR 14408