stocks: add expand_all to stocks interface

[emreduzenli]

Fixes #5338

[ab9rf]

I'm uncertain that this is the correct thing to do here, but I also don't understand why collapse_all does the same thing. So if someone could explain this to me, it would help me feel better about approving this change.

[chdoc]

I think you were right to be suspicious. stocks.i_height appears to be the total height of the right hand side (in interface lines, 3 per entry). When expanding all entries, the total height of the right inside could be computed as simply as:

Suggested change

	stocks.i_height = num_sections * 3
	num_items = #stocks.current_type_i_list
	stocks.i_height = (num_items + num_sections) * 3

[emreduzenli]

thank you for the clarification, I've updated the branch to reflect your suggested way of computing it