Only show Google Tasks that are parents and fix ordering

[allenporter]

Proposed change

Order Google Task To-do items using the server side ordering. Google Tasks that are siblings are sorted using the "position" string.

In discussion with product leads, we want to filter out child tasks and not show them since they are not supported in the UI.
A future upcoming (soon) PR will support task re-ordering. We can reconsider support for parent/child tasks in the future.

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[allenporter]

Note differing behavior in #103809 we should probably reconcile.

[allenporter]

From an offline discussion, we've decided that we should not support child tasks.

[frenck]

Nice! Thanks, @allenporter 👍

../Frenck