JIT: inline `char->integer' and `integer->char'
racket/draw win32: work around a Pango bug

Pango crashes (with an assertion failure) on characters U+1D173
through U+1D17A. Trying to fix (or even just compile) Pango for
Windows is hard, so skip the characters at the `draw-text' and
`text-extent' level.

The bug is unlikely to be specific to just those characters in the
long run, but only those characters appear to be problematic on my
Windows 7 installation. So, the workaround may be enough for many
installations, and hopefully the Pango bug wil be fixed one day.

Relevant to PR 13513