Use consistent language for "states"

[Tc-Fast]

Related to #2052

[chrbertsch]

Torsten S: I will provide a suggestion based on this, where we have consistency with usage in the XML. I will diskuss this with @Tc-Fast

[chrbertsch]

FMI Design meeting:

We suggest to limit this PR to only make the distinction between state machine modes and other states.
There are more changes necessary to fix inconsistencies w.r.t. continuous(-time), discrete(-time) and clocked variables and states that should be done in a different PR.

[chrbertsch]

Christian: This means something different ...
Klaus: it is the same "state" as in "get state" --> "the internal FMU state"
Christian: in many places it is just called "FMU state". Should we get rid of the "internal"?

[Tc-Fast]

I changed the commit to now only include the distinction between "state machine modes" and other "states".

[chrbertsch]

FMI Design Meeting:
Torsten S: I work on a larger PR to clean up the usage of "state". Could we wait with merging this one?

[chrbertsch]

@Tc-Fast : should we not leave this open as draft PR until @t-sommer suggests his proposal?

[Tc-Fast]

I accidently closed it, by deleting my branch. I guess i should use better branch names.