Use task icons in gscan, not job icons.

[hjoliver]

This is a small change with no associated Issue.

As discussed in Element chat, the gscan panel shows task states represented by job icons. Arguably this is a bug, even though it was deliberate, because task and jobs states are not quite the same thing even where they seemingly coincide. We apparently discussed this early in the project and decided to use job icons in gscan because:

• for the important states, there is a one-to-one mapping between task and job state
• coloured icons are better at-a-glance indicators
• existing users have been conditioned to seeing coloured icons, by the old Cylc 7 gscan GUI

However, the one-to-one mapping is somewhat beside the point in the case of retrying tasks, and I have evidence (a "bug" report) that users may find this confusing.

User: "gscan showed no failed tasks, but when I opened the workflow there was a failed task[sic] in it".

On this branch:

(NB the task progress bar is not relevant here, would need to get rid of that of course).

This still requires users to understand the difference between task and job icons, but unlike in the first case it is not potentially confusing once you do understand that.

So IMO we should change this. If others are super attached to a colourful gscan, we should consider making that a user preference (next to which we can document the failed job retrying task "subtlety" that results).

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).

• Appropriate tests are included (unit and/or functional).
• Already covered by existing tests.
• Does not need tests (why?).

• Appropriate change log entry included.
• No change log entry required (why? e.g. invisible to users).

• I have opened a documentation PR at cylc/cylc-doc/pull/XXXX.
• No documentation update required.

[hjoliver]

(Deleted comment on possibly adding a waiting icon to gscan as well ... that would be useful to distinguish between "nothing happening, stalled" and "nothing happening, waiting on an xtrigger", but it might be confusing to see no waiting tasks at all most of the time when not stalled or about to finish, as is often the case under spawn-on-demand).

[hjoliver]

(August meeting discussion: agreed that we need to resolve the current inconsistent use of icons, but the way forward still needs more thought.)