[API] Add missing types to the code

[JerrySentry]

mypy_results.txt Add typing to all function arguments and returns.

{
    'no-untyped-def': 4089, 
    'var-annotated': 12, 
    'arg-type': 81, 
    'valid-type': 2, 
    'return': 26, 
    'assignment': 23, 
    'return-value': 49, 
    'misc': 19, 
    'dict-item': 13, 
    'name-defined': 1, 
    'no-redef': 4, 
    'method-assign': 1, 
    'index': 1, 
    'syntax': 1, 
    'operator': 2, 
    'has-type': 2, 
    'override': 1, 
    'union-attr': 6, 
    'list-item': 1,
    'func-returns-value': 2
}

[JerrySentry]

Going to close this. It's not viable at all to add typing to 4000+ missing type defs in the repo. Instead the strategy is to have developers add missing types to files they touch in their PRs (even if it has no relationship on the lines of code they've touched in the file). Initially it will be a light prodding (ie will not disallow merging) but still only display as failed in CI and on pre-commit. Eventually will change this to blocking with enough feedback.