Merge pull request #2680 from lambdageek/dev/reflection-no-loadererror

Merge pull request #2680 from lambdageek/dev/reflection-no-loadererror

[reflection] Get rid of loader error in reflection.c

Get rid of (direct and indirect) calls to `mono_loader_set_error_from_mono_error` in reflection.c:

- `mono_custom_attrs_from_index`
- `mono_custom_attrs_from_method`
- `mono_custom_attrs_from_class`
- `mono_custom_attrs_from_assembly`
- `mono_custom_attrs_from_module`
- `mono_custom_attrs_from_property`
- `mono_custom_attrs_from_event`
- `mono_custom_attrs_from_field`
- `mono_custom_attrs_from_param`

In all the functions, add a `_checked` variant that has a `MonoError*` out argument and for the  MONO_API functions.  The public API versions just clean up the error and return NULL.  Loader error isn't touched anymore.