IntelliJ generated sources content root and file watcher

This automatically refreshes the generated source files, and the
generated sources folder now has a nice icon.

Potential conflict if anyone uses IntelliJ without the container
(which I'm not aware of).

Test Plan: Modified protobuf file, generated sources were automatically refreshed.

X-Origin-Diff: phab/D234
GitOrigin-RevId: 5f5eb7f2cf541c7dd143564dcad4885476b4bfb0
diff --git a/scripts/rebuild_generated.sh b/scripts/rebuild_generated.sh
new file mode 100755
index 0000000..8edcf65
--- /dev/null
+++ b/scripts/rebuild_generated.sh
@@ -0,0 +1,2 @@
+#!/bin/bash
+bazel build core/api/... && scripts/bazel_copy_generated_for_ide.sh