Also fixes incorrect location of `tv_dict_add` function and three bugs in other
functions:
1. `tv_dict_add_list` may free list it does not own (vim/vim#1555).
2. `tv_dict_add_dict` may free dictionary it does not own (vim/vim#1555).
3. `tv_dict_add_dict` ignores `key_len` argument.
Looks like dict_notifications_spec test used to depend on some state which
should not be preserved. Changed all `setup()` calls to `before_each()` and
added necessary state in addition to changes required to test empty keys.
Note: unit tests for tv_dict_watcher* are still needed.
Additional modifications:
- More `const` qualifiers in tested functions.
- `tv_list_find_str()` second argument is more in-line with other
`tv_list_find*()` functions.
Tests crash at some point without
- `after_each(collectgarbage)` right before “typval.c list copy() copies list
correctly and converts items” test.
- Commenting out that test.
- Adding `collectgarbage()` after the test (what actually this commit does).
Adding `collectgarbage()` to top-level `after_each` block right after
`restore_allocators` makes running this file crash even if it is run alone.
For now it is full of FIXMEs and tests for incorrect behaviour. Sorted out to
have FIXMEs in one place, commented crashing tests in other and correctly
working tests in the third one.
Also found some bugs:
1. var_item_copy() always fails to copy v:_null_list and v:_null_dict. Fixing
this should mean fixing `deepcopy(v:_null_list)` which should’ve been, but
was not listed in #4615. This also fixes `deepcopy(v:_null_dict)`.
2. var_item_copy() crashes when trying to copy NULL string with `conv != NULL`.
3. `conv` argument is ignored when copying list unless `deep` is true, but it
was not reflected in documentation.
4. `tv_dict_item_alloc_len()` allocated more memory then needed.
5. typvalt2lua was not able to handle self-referencing containers.
