ST provides a default wrap_block
command which does something like that based on indentation levels.
The default binding for it is
{ "keys": ["{"], "command": "wrap_block", "args": {"begin": "{", "end": "}"}, "context":
[
{ "key": "indented_block", "match_all": true },
{ "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
{ "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
{ "key": "following_text", "operator": "regex_match", "operand": "^$", "match_all": true },
]
},
Not sure what sets indented_block
though.