fork-and-rename takes a long time to rename

[gordonwoodhull]

(this is an old bug, not related to the editor tab refactor. but it would be nice to deal with it now.)

start renaming the current notebook and press ctrl/cmd enter to fork under the new name.

even though you own this notebook and it's going through the special don't-fork-copy case, it first renames the notebook to "current name 2" and then a moment later it renames to the name you chose.

while this works, this is not confidence-inspiring. since we are creating a brand-new notebooks, we should not need to fork and rename as separate steps - we should just use the new name from the start.

this may mean some extra parameters passed around or other special cases, but we shouldn't burden the user with these internal details.

[gordonwoodhull]

the effect is similar to the copy-then-delete annoyance in the asset pane #735. not the same root cause in the code, but also caused by lazy implementation of the API.