Support talon API for inserting and wrapping with snippets

[pokey]

Something like the following:

def insert_named_snippet(name: str, target: Optional[Target] = None):
    """Inserts a named snippet"""
    pass

def insert_custom_snippet(body: str, target: Optional[Target] = None, scope: Optional[str] = None):
    """Inserts a custom snippet"""
    # Note that we convert scope to a proper scopeType; technically it is a scopeTypeType
    pass

def wrap_with_named_snippet(name: str, variable_name: str, target: Target):
    """Wrap target with a named snippet"""
    pass

def wrap_with_custom_snippet(body: str, target: Target, scope: Optional[str] = None, variable_name: Optional[str] = None):
    """Wrap target with a custom snippet"""
    pass