"Erase output" UI on each code block

[Sleepful]

currently there is an "Erase output" button at the top of a notebook which requires scrolling and deletes every output, it would also be nice to delete the output of a given code block only

[jonatanklosko]

This is intentional, erasing all outputs effectively resets the evaluation, so everything needs to be executed from scratch. It may make more sense in notebook systems where cells are evaluated independently, but since we guarantee sequential evaluation, removing a single output would lead to a unintuitive state, where an output is kinda missing.