Update prev/next unresolved thread icons

Purpose

• Update icons to use chevrons instead of angles (angles still use the old icon weight and will be deprecated).
• Use "Go" instead of "Jump" for the action in the tooltip so that it's more clear and concise.

Note:

• Color change isn't part of this, it's just related to the type of MR.
• Replacing "jump" with "go" in the click actions (For example, @click="jumpToPreviousDiscussion") is out of scope for this change.

Before	After

Related to #362500 (closed)