Config form list items really don't look right when the content for the

item is more than one line. The icon, content, state indicator, and

actions are all set to vertically-align by default, and when there's

content that grows vertically, everything else looks wrong. We've had

styling in other places that tried to work around this, but each place

had to override things in their own way, and that's not good for future

maintenance.
This change aims to fix this by introducing new modifiers that flag an

item (or a list of items) as having multi-line content. This has the

effect of anchoring state columns and actions to the top of the item,

laying out actions vertically instead of horizontally, and allowing a

main content area to have a reasonable line height and to wrap normally

(instead of the default of ellipsizing).
To activate this, the list should use an -all-items-are-multiline

modifier, or individual items can use -is-multiline. The main content

area of an item containing the multi-line content should then be wrapped

in a djblets-c-config-forms-list__item-main class.

Tested this with the new extensions UI rewrite, which makes use of

multiline content. Verified that all layout looked completely

reasonable.
Tested standard lists, and saw that they continued to look correct.