[kairos] rename many APIs

* TState -> State
* TFlow -> Events
* FrpBuildScope -> BuildScope
* FrpStateScope -> StateScope
* FrpTransactionScope -> TransactionScope
* FrpEffectScope -> EffectScope
* FrpScope -> KairosScope

etc.

Flag: EXEMPT unused
Test: atest kairos-tests
Change-Id: I56eb686be46833539c93d8c56c5a2eec93af54b6