Create new block for final instructions inserted into a lambda

Summary:
CPython will usually insert a `LOAD_CONST`/`RETURN_VALUE` at the end of a lambda, and then this will get optimized away. This has a side effect of leaving a `None` const on the lambda.

We emit it in the same block currently which can prevent some other optimizations because we'll see the return block as being too large.

Reviewed By: jbower-fb

Differential Revision: D81977406

fbshipit-source-id: e6cccd87799330b3d65534f9ed6ed5c4c13b6b23

Author: DinoV

cinderx/PythonLib/cinderx/compiler/pycodegen.py

@@ -4547,6 +4547,7 @@ def generate_function_with_body(
             else:
                 gen.set_pos(SrcLocation(node.lineno, node.lineno or 0, 0, 0))
             gen.emit("RETURN_VALUE")
+            gen.nextBlock()
             gen.finish_function()
         else:
             if isinstance(node, ast.Lambda):

cinderx/PythonLib/test_cinderx/test_compiler/testcorpus/20_lambda_ifexp.py

@@ -0,0 +1,4 @@
+lambda oparg, jmp: ((
+            2 if oparg[0] in ("1", "2") else 1
+        )
+        - 3)