docs: Add deprecation guide
buildxpi: restore `--disable-compile-environment`

Mozbug 862770 has already been fixed.
properties: handle \uNN

Slight change in processing to make sure that we don't bitshift if the
char is not a hex char.  The code worked otherwise.

Note: Java does not support \uNN or \uNNN.  But it can't hurt to support
this in either.
properties: escape leading and trailing spaces

Otherwise Mozilla’s parser will “eat” them.
docs: update Wikipedia as part of release process