fix module browser for submodules
add module-browser test (should have been included in 6949473b)
make the module browser report the search result counts
and, when the search string is empty, the total number of modules
use --deps search-auto for "Available from Catalog" installs
in the GUI package manager

closes PR 14444
compile: fix namespace leak related to submodules and compilation

A reference intended to be temporary from a submodule to its enclosing
module wasn't NULLed out.
fix stepper-skipto annotation for test expansion
provide a more helpful message on failure of syntax traversal in the stepper
rackety, add a test for annotation success on test cases in the stepper
comments, rackunit-y
Fix type of sequence-filter.
Fix RacketCon date on web page.
fix benchmark timeout time
add 10 sec heartbeat to benchmark logging

also, enable caching by default
log major gcs in benchmark
Rackety (line lengths)
improve ellipsis-related error messages

closes PR 14435
added -existing- to error message to help programmers understand that they must specify the name of an existing file
fix error message again after consulting with SK
fixed source location reporting, test annotation; Rackety tests
include a phase summary in module browser