This commit rewrites deno_core::JsRuntime to not implement Future
trait.
Instead there are two separate methods:
- JsRuntime::poll_event_loop() - does single tick of event loop
- JsRuntime::run_event_loop() - runs event loop to completion
deno_core/
- rename core_isolate.rs to runtime.rs
- rename CoreIsolate to JsRuntime
- rename JSError to JsError
- rename JSStackFrame to JsStackFrame
cli/
- update references from deno_core::CoreIsolate to deno_core::JsRuntime
- rename deno_core::JSError to deno_core::JsError
- rename fmt_errors::JSError to fmt_errors::JsError
