js: Fix return values of not-really-infallible functions

While refactoring object.cpp I noticed that gjs_define_object_class()
doesn't do proper error checking; the JSAPI functions used within it can
throw, but it doesn't check that.

Fixing this also had a cascade effect on
gjs_object_define_static_methods() and gjs_define_param_class(), as well
as some code in fundamental.cpp and repo.cpp.

Similarly, find_vfunc_info() in object.cpp could also throw but the
return value was never checked.
18 jobs for refactor-object-instance2 in 32 minutes and 40 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Source Check
passed #46937
cppcheck

00:03:37

passed #46938
cpplint

00:04:54

passed #46939
eslint

00:03:46

passed #46936
fedora

00:02:32

 
  Test
passed #46940
fedora_clang

00:06:19

 
  Thorough Tests
manual #46952
allowed to fail manual
armv8
passed #46943
coverage

00:04:52

passed #46942
installed_tests

00:04:18

manual #46948
allowed to fail manual
lts
manual #46947
allowed to fail manual
no_graphics
passed #46941
no_profiler

00:05:06

passed #46944
sanitizer_gcc

00:21:08

manual #46946
allowed to fail manual
valgrind
passed #46945
with_logging

00:03:32

manual #46951
allowed to fail manual
zeal_11
manual #46949
allowed to fail manual
zeal_2
manual #46950
allowed to fail manual
zeal_4
 
  Delivery
manual #46953
allowed to fail manual
packaging