This makes 'test.' an implicit package prefix, thus fixing the inspection
"Package directive doesn't match file location" positive in almost all
test files.
* It enables subtyping relationship for keys and elements, allowing type-safe and concise manipulations on the context when complex hierarchies of elements (e.g. implementors of ContinuationInterceptor) are present
* It unblocks possibility to implement suspendCancellableCoroutine in stdlib
* Implementing proper polymorphic get and minusKey in AbstractCoroutineContextElement is impossible because it will introduce source-incompatible change
* ContinuationInterceptor get and minusKey are adjusted in a completely backwards-compatible way
This introduces new functions instead of the existing sequence builders:
- `sequence` instead of `buildSequence`
- `iterator` instead of `buildIterator`
- `SequenceScope` instead of `SequenceBuilder`
The old functions were deprecated with error and made inline-only, and `SequenceBuilder` has been
made a deprecated typealias to `SequenceScope`.
Move sequence builders to `SequencesKt` facade class.
Replace sequence builder usages in stdlib and samples.
#KT-26678
* The members of Result are isSuccess, isFailure, exceptionOrNull, getOrNull
* The rest of API is implemented via inline-only extensions
* There are two internal functions to hide detailed mechanics of an internal
Result.Failure class: createFailure and throwOnFailure
* Result.toString is explicit: either Success(v) or Failure(x)
See KT-26538
ContinuationInterceptor companion object is named Key
CoroutineContext.Element property for key is named just key
AbstractCoroutineContextElement implements all of CoroutineContext.Element, including key
Ilya Gorbunov