[REFACTOR] Use more TypedPackedFuncs (#2981)

[REFACTOR] Use more TypedPackedFuncs (#2981)

* Add `set_body_simple` to Registry, refactor a lot of code to use it

* Add more types to Relay PackedFuncs

* Add Registry::set_body_method to easily make Node methods into
PackedFuncs

* Add set_body_method, set_body_node_method; start typing api_lang

* Add some docs, remove unused script

* Fix mysterious linter problem

* Touch up api_ir.cc

* Fix some issues with TOPI argument counts

* Revert changes to topi.cc to avoid problems with optional arguments

* A little more cleanup

* Type more of the api _ functions

* Whitespace

* Finalize names and docs for new registry helpers

* Update docs