build: Pull pacrunner forward to mozjs38

Mozjs185 is getting really old and unsupported. Newer versions
of the mozjs JSAPI are C++ based. So we convert the plugin to
C++ and then apply necessarily API changes so that it can be built
with the more recent mozjs38. For example we now need to "root"
values being passed into the API in order to satisfy the JSAPI
garbage collection rules. Further, a number of the APIs have been
tweaked and moved into the JS namespace, so we namespace them
appropriately and adjust their parameters.
4 files changed