Support non-interactive editing of State and Signaling diagrams

[vareb]

Goal: be at least as good as the official PlantUML online tool for editing state diagrams. That is, no right-side interactivity, but at least we shouldn't crash or hang.
For example, we produce an error if we have the following diagram:

@startuml
state Identify_GTP_C_message
@enduml

Hovering over the participants also displays an error.

Solution proposal: identify if the diagram is currently an Activity diagram and then enable all the right-side features, otherwise disable them all. PlantUML itself does this identification when converting the diagrams, so it is possible.

[Godsmith]

@vareb I deployed, but still get the error popups? https://pdupc-pcsmplantuml.sero.wh.rnd.internal.ericsson.com/?SoWkIImgAStDuG8oIb8LF5DIyqeoqohZtKC2uftZSrEBYnFJKxaSKlDIW8e0

[Godsmith]

Nevermind, I ran into #5 >_< We should prioritize that.

[Godsmith]

Reopening this again. This signaling diagram still gives errors:

https://pdupc-pcsmplantuml.sero.wh.rnd.internal.ericsson.com/?SoWkIImgAStDuKhCAL58r5F8J5F8orS8BKX9B4dbIbJGjLD8uahDIr40IdCv01b0fG0=

@startuml
alt a. if no Update
a -> b
end alt
@enduml

"end" should not be a inclusion criteria here: https://github.com/Ericsson/PlantUML-Interactive-Editor/blob/main/src/plantuml_gui/static/script.js#L3545C5-L3545C103 ; it is actually used in both sequence diagram (for blocks), use case diagrams and state diagrams (for notes)

"start" seems to still be fine though.