Fix dragging topic names with special characters to the Image panel

[jtbandes]

User-Facing Changes
Fixed an issue with dragging and dropping topics into the Image panel if the topic names contain special characters.

Description
The path field is quoted, but the Image panel uses an unquoted topic name in its config, so drag & drop would result in an invalid config if the topic name required quotes. This fixes the issue by adding a new topicName field to pass through the unmodified topic name.

[defunctzombie]

It kinda looks like we've already parsed the path somewhere to get the topicName? Or maybe that's from the list of topics itself?

Would rootTopicName make more sense to align with rootSchemaName?

Does seem somewhat awkward to see "isTopic: false" and then you have a topic name - I guess that tells you if the path itself is a topic? Why doesn't the receiver figure that out itself? Should the parsed path AST be sent instead?

[jtbandes]

Should the parsed path AST be sent instead?

Might be nice but the thought was to eventually publish this in the extension API and I believe we haven’t reworked our “RosPath” to a place where we’re comfortable with publishing it.

[jtbandes]

Would rootTopicName make more sense to align with rootSchemaName?

I don't feel too strongly either way. My thinking on this was that rootSchemaName makes some sense because you could imagine a schema for each sub-message, and this one refers to the root. On the other hand, with topics, there are no "nested topics" – there is just one topic at the root level.