Display blocking issue count on issues in list

Problem to solve

Based on #34247 (comment 285026817) this change displays, next to each issue in the list, the number of issues it is blocking.

It is a first iteration towards sorting the issues list on this value (see: #34247 (closed)).

Proposal

...we would like to add Blocking information within issue list items, so once a user sorts by Blocking, they can easily scan these values. As seen in this design, we propose adding the issue-block icon, followed by the number of issues it is blocking. Hovering over the icon or value would display a tooltip informing the user what this information represents (as seen here).

Links / references