Targets can now be configured add exec_properties on top of the platform's exec_properties
See https://docs.google.com/document/d/1w3fu8zu_sRw_gK1dFAvkY2suhbQQ82tc0zdjet-dpCI/edit#heading=h.5mcn15i0e1ch

RELNOTES: introducing per-target exec_properties
PiperOrigin-RevId: 265540815
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index 0a08231..e23e491 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -136,6 +136,7 @@
   public static final PathFragment THIRD_PARTY_PREFIX = PathFragment.create("third_party");
   public static final PathFragment EXPERIMENTAL_PREFIX = PathFragment.create("experimental");
   public static final String EXEC_COMPATIBLE_WITH_ATTR = "exec_compatible_with";
+  public static final String EXEC_PROPERTIES = "exec_properties";
 
   /**
    * A constraint for the package name of the Rule instances.