More explicit form usage

[egekorkan]

Basically the proposal in #2175 as a PR for change tracking

[egekorkan]

TD Call today:

• The concern of @benfrancis is not exactly understood even though the problem is understood.
• It will make it simpler for Scripting API to use formIndex as the length and order of forms do not change.
• While we lose the ability for "This device can be used with protocol A most of the time", giving any guarantees requires profiling mechanism.
• It will make it simpler to implement expansion algorithms.
• Also see alternative direction: [Common Definitions] Only allow one default Form in formDefaults #2175 (comment)