Show placeholder hints for different entry boxes

[Ezio-Sarthak]

We've fairly improved the styling of compose boxes (#783/ #852/ #865), though we could improve more upon the same, by adding context to them. Currently, # and > are the only indicators (for an end-user) to know that a box is of stream or topic, respectively. The same is the case for PM recipients box (To), and (visually) no context for the message write box.

As there could be various approaches to explore, feel free to discuss them on CZO in the thread: #zulip-terminal > Contextual hint text for compose boxes

To mention one of the approaches, I tried adding a wrapper class for WriteBox.

[zulipbot]

ERROR: Label "UI" does not exist and was thus not added to this issue.

[neiljp]

Rereading this, I wanted to clarify that my understanding is that the contextual hints could be text that is shown until the user starts typing in a box, a little like the web app shows Topic in that entry box when composing, which disappears when entering text.

However, I'd suggest looking at the linked topic above and related discussions to confirm.