[Feature Request] Enable notifying lang in realtime of local activity resolutions

[Sushisource]

Right now Core will wait until all outstanding LAs within a task have finished (or we're about to report the WFT b/c we're near the timeout) before telling lang about LA resolutions.

This prevents you from efficiently running one LA that takes a long time in parallel with many short LAs that run in sequence.

See the test added here, make it work such that all the sequential LAs complete in the first WFT.

Consider also reviewing https://github.com/temporalio/sdk-core/issues/449 and closing out anything that might be remaining there while doing this.