* Implement Nucleus::createCoroutine and acquireCoroutine so that they
create a regular function for the Begin entry, and stubbed functions
for the Await and Destroy entries.
* Made Routine::getEntry const as Coroutine expects this function to
be callable from multiple threads. Subzero's implementation would
lazily finalize the entry and cache it. Now we finalize it eagerly in
acquireRoutine, and getEntry simply returns pointers.

Bug: b/130459196
Change-Id: Id9fa447ce55c7df6fb55e1c878ca021e825fecfa
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38873
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>