util: format add %t placeholder for calling inspect to serialize

`util.format` add `%t` placeholder for calling `inspect` to serialize object

* This is very convenient for calling `util.inspect` method in `util.format`.
* Compared with json(`%j`), it can be serialized width `customInspect` opt. It is useful for serializing other Object (eg: `Data`) in format.
Minor style issue: opening brace should be on same line as function keyword.