Add ExecGroupCollection and ExecGroupContext objects to starlark for ctx.exec_groups[<exec_group>] and ctx.exec_groups[<exec_group>].toolchains[<toolchain_type>] access respectively

WANT_LGTM=all
PiperOrigin-RevId: 307697565
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
index b7d35bf..0bccc31 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
@@ -1229,7 +1229,7 @@
   }
 
   @Nullable
-  public ToolchainCollection<ResolvedToolchainContext> getToolchainContextsForTesting() {
+  public ToolchainCollection<ResolvedToolchainContext> getToolchainContexts() {
     return toolchainContexts;
   }