Allow rule writers to create exec_group related exec transitions via config.exec(exec_group) and attach them to starlark dependency attrs.

PiperOrigin-RevId: 308290724
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BUILD b/src/main/java/com/google/devtools/build/lib/analysis/BUILD
index 92efb5b..4de5d46 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BUILD
@@ -1557,9 +1557,11 @@
         ":config/transitions/patch_transition",
         ":config/transitions/transition_factory",
         ":platform_options",
+        ":toolchain_collection",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
         "//src/main/java/com/google/devtools/build/lib/events",
         "//src/main/java/com/google/devtools/build/lib/packages",
+        "//src/main/java/com/google/devtools/build/lib/skylarkbuildapi",
         "//third_party:guava",
         "//third_party:jsr305",
     ],
@@ -2035,6 +2037,7 @@
     name = "skylark/starlark_config",
     srcs = ["skylark/StarlarkConfig.java"],
     deps = [
+        ":config/execution_transition_factory",
         "//src/main/java/com/google/devtools/build/lib/packages",
         "//src/main/java/com/google/devtools/build/lib/packages:type",
         "//src/main/java/com/google/devtools/build/lib/skylarkbuildapi",