runtime: use the tasks scheduler instead of coroutines

This results in smaller and likely more efficient code. It does require
some architecture specific code for each architecture, but I've kept the
amount of code as small as possible.

targets/nintendoswitch.json

@@ -1,6 +1,7 @@
 {
   "llvm-target": "aarch64",
   "build-tags": ["nintendoswitch", "arm64"],
+  "scheduler": "tasks",
   "goos": "linux",
   "goarch": "arm64",
   "linker": "ld.lld",
@@ -9,6 +10,7 @@
   "gc": "conservative",
   "relocation-model": "pic",
   "cpu": "cortex-a57",
+  "default-stack-size": 2048,
   "cflags": [
     "-target", "aarch64-unknown-none",
     "-mcpu=cortex-a57",
@@ -26,6 +28,7 @@
   "linkerscript": "targets/nintendoswitch.ld",
   "extra-files": [
     "targets/nintendoswitch.s",
+    "src/internal/task/task_stack_arm64.S",
     "src/runtime/gc_arm64.S",
     "src/runtime/runtime_nintendoswitch.s"
   ]