extmod/asyncio/uasyncio.py: Add backwards-compatible uasyncio alias.

This allows existing code that does `import uasyncio` or
`import uasyncio as asyncio` to continue working.

It uses the same lazy-loading as asyncio to prevent loading of unused
features.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tests/extmod/asyncio_as_uasyncio.py

@@ -0,0 +1,12 @@
+try:
+    import uasyncio
+    import asyncio
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+x = set(dir(uasyncio))
+y = set(dir(asyncio)) - set(["event", "lock", "stream", "funcs"])
+
+print(x - y)
+print(y - x)