librustc_trans and librustdoc: add license::print().

The license document is compressed by DEFLATE and then stored as
pub const license::text::COPYRIGHT of type &'static [u8].
A helper script src/etc/license2rs.sh takes care of updating it.

It is decompressed by flate::inflate_bytes() on runtime.

Fix #17690

Signed-off-by: NODA, Kai <nodakai@gmail.com>