exp/cmd/gosym: implement wcontext.addGlobals
exp/cmd/gosym: implement wcontext.addGlobals

gonotes/godef,tw4452852/godef,pepin/godef,grafov/godef,ManojkumarV/godef,cmars/tools,lukehoban/godef,abourget/godef,rogpeppe/godef,cmars/tools,cmars/tools,cmars/tools