Support nested expressions in state actions

[treiher]

Nested expressions are rarely supported in state actions. A workaround for this limitation is the use of separate assignments for the nested expressions (e.g., T := M.F; F (T); instead of F (M.F);).

Examples

• Function call as argument of a message aggregate
• Message field access as argument of a message aggregate
• #979
• #1018
• #1063