racket/gui: fixups for mod3-5 event additions

Move new initialization arguments to the end to avoid backward
incompatibility, add fields to `module-event%`, and include history
notes in the documentation.
Minor doc fixes in Reference and Inside
racket/gui: add [set-]undo-preserves-all-history[?] to editor<%>

This change allows undo configuration of individuals editors to
Emacs-style undo (in addition to the 'GRacket:emacs-undo global
preference that is read on startup).

Also, fix a bug in Emacs-style undo that dates from the port of
the editor into Racket.
fix another potential overflow in fixnum `expt`

This commit is a follow-up to e96d592735. The bug fixed this time is
more subtle, because the overflowing computation is never used, but
that doesn't matter in terms of avoiding undefined behavior.

Thanks for Pascal Cuoq and John Regehr.
unix-style install: preserve build stamp

Instead of preserving specific configuration entries, it's probably
better to preserve all of them that are not specifically replaced.
I'm going with the simpler change for now, though.
Check kw function definitions w/o type annotations

Instead of trying to check the expansion as-is (which
always fails), check the core function and reconstruct the
keyword function type.

Closes PR 11253
Handle kw λs when useful annotations are missing

Closes PR 14322
move the class/c implementation into its own file
add missing export
Remove extra in-set type annotation.
srfi/34: work with `else` frmo `racket` or `mzscheme`
add one more missing require from recent class/c file rearrangement
minor clarification to specify #:opaque more fully
Update typed/net/url

Closes PR 14330
v5.93 installers info
Synch German string constants with latest.
document parameter settings of a new place
raco setup: fix test for installing doc CSS to user-specific location

For example, if a package is installed in user scope where no
user-scope documentation is already built, CSS files need to be
in place for the main page of user-specific documentation.
edito
break up class/c's representation into the internal and external parts

The main change in this commit is to refactor the class/c projection
such that it actually build two classes internally when only a single
class/c is applied to a single class. The goal is to further adjust
class/c so that the projection corresponding to the external method
contracts goes away (to be replaced by a new strategy) and the
projection corresponding to the internal method contracts gets delayed
using some as-yet-underminded strategy that avoids creating the new
class until someone actually creates a subclass.

This commit, but itself, however is a performance lose to the tune of
about 2 megabytes in DrRacket's startup footprint. Hopefully this
doesn't last too long.