UI: Add chips to ease navigation to the Tasks tab

On changes with a lot of label scores or changed files, users
have to scroll to view status of their tasks. This change adds
a chip (under the commit message, similar to comment chips)
each for 'needs' (aka ready) and 'blocked' (aka failed) tasks
to ease navigation and to show a quick summary of tasks. Here
are some highlights:

 - Chips are shown only after the tasks have loaded
 - Clicking the chips changes focus to the Tasks tab
 - Each chip shows the count of respective tasks
 - Chips are hidden if the count of respective tasks is 0
 - Warning style is used for 'needs' chip and error for 'blocked'

Also, update the eslint ecmaVersion[1] to 2020 to support optional
chaining.

[1] https://eslint.org/blog/2020/07/eslint-v7.5.0-released/#optional-chaining-support

Change-Id: I3e69232661577b64064ce03627cf7efb86728c81
7 files changed