[antlir][shape] make test shape use in-tree build of bzl2ir

Summary: Split out from D57445425 because this rebuilds the entire world.

Test Plan:
```
❯ buck2 test fbcode//antlir/bzl/tests/shapes/...
Buck UI: https://www.internalfb.com/buck2/941f3f04-989f-4abf-8669-eaf95387012f
Test UI: https://www.internalfb.com/intern/testinfra/testrun/4222124882748834
Note:    Using experimental modern dice
Network: Up: 679KiB  Down: 105MiB  (reSessionID-cd18ec0a-2f8d-471a-91f8-db42fdb10be3)
Jobs completed: 2297. Time elapsed: 11.0s.
Cache hits: 97%. Commands: 366 (cached: 354, remote: 0, local: 12)
Tests finished: Pass 24. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Reviewed By: zeroxoneb

Differential Revision: D57495481

fbshipit-source-id: 17e8fd9c9df4cf1cbda666a74f468bf505ab7cf2

antlir/bzl/shape.bzl

@@ -230,20 +230,25 @@ def _shape(__thrift = None, **fields):
 
     return record(**fields)
 
-def _impl(name, deps = (), visibility = None, expert_only_custom_impl = False, **kwargs):  # pragma: no cover
+def _impl(name, deps = (), visibility = None, expert_only_custom_impl = False, test_only_rc_bzl2_ir: bool = False, **kwargs):  # pragma: no cover
     if not name.endswith(".shape"):
         fail("shape.impl target must be named with a .shape suffix")
     export_file(
         name = name + ".bzl",
     )
 
+    # @oss-disable
+
+    bzl2ir = antlir_dep("bzl/shape2:bzl2ir") # @oss-enable
+    if test_only_rc_bzl2_ir:
+        bzl2ir = antlir_dep("bzl/shape2:bzl2ir")
+
     buck_genrule(
         name = name,
         cmd = """
             $(exe {}) {} $(location :{}.bzl) {} > $OUT
         """.format(
-            # @oss-disable
-            antlir_dep("bzl/shape2:bzl2ir"), # @oss-enable
+            bzl2ir,
             normalize_target(":" + name),
             name,
             shell.quote(repr({d: "$(location {})".format(d) for d in deps})),

antlir/bzl/tests/shapes/BUCK

@@ -12,6 +12,7 @@ oncall("antlir")
 shape.impl(
     name = "test.shape",
     rust_crate = "test_shape",
+    test_only_rc_bzl2_ir = True,
     deps = [
         "//antlir/bzl:target.shape",
     ],

antlir/bzl/tests/shapes/test.shape.bzl

@@ -3,8 +3,8 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
-load("//antlir/bzl:shape.bzl", "shape")
-load("//antlir/bzl:target.shape.bzl", "target_t")
+load("@antlir//antlir/bzl:shape.bzl", "shape")
+load("@antlir//antlir/bzl:target.shape.bzl", "target_t")
 
 affiliations_t = shape.shape(
     faction = str,