Rename some ClassObject/Provider-related methods

The terminology "field" is preferred over "key" for the components of a struct or struct-like object.

RELNOTES: None
PiperOrigin-RevId: 180269374
diff --git a/src/main/java/com/google/devtools/build/lib/packages/NativeInfo.java b/src/main/java/com/google/devtools/build/lib/packages/NativeInfo.java
index d52fa87..e1035c8 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/NativeInfo.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/NativeInfo.java
@@ -29,12 +29,12 @@
   }
 
   @Override
-  public boolean hasKey(String name) {
+  public boolean hasField(String name) {
     return values.containsKey(name);
   }
 
   @Override
-  public ImmutableCollection<String> getKeys() {
+  public ImmutableCollection<String> getFieldNames() {
     return values.keySet();
   }