lexers it defers to
also, remove the checks in color.rkt in the framework (they are not
all covered by the added contract, but they mostly are and when they
aren't, most of those times are using the heavily tested racket-lexer)
and change the tests so they all run with port line
counting enabled (or else the unicode test fails)
adjust module-lexer.rkt tests so they can run in either
port-counting mode or not (but currently run them all in
port-counting mode because scheme-lexer doesn't work without it)
also make a first stab at what needs to change in the module
lexer to make it work in non port line-counting mode
'read-language' uses as a single token in the case that read-language
fails. This helps it to deal with things like s-exp and at-exp
properly
closes PR 12260
