bazel packages: move lib.syntax.Type here

Type is a concept of the build language, not of core Starlark.
(Witness all the references to Label. That said, there appear to be
three concepts---BuildType, Type, StarlarkType---where only two
are necessary: the types of rule attributes, and a library of
Starlark-to-Java conversion combinators.)

This change is mostly mechanical, except:
- MethodLibrary: two uses of Type.XYZ.convert replaced by ad-hoc code.
- SkylarkDict: getDictFromArgs substantially rewritten to avoid Type.
  Its error messages were improved.
  I added comments re: harmful type parameterization.

This CL depends on unknown commit, which first breaks
Copybara's dependency on syntax.Type.

PiperOrigin-RevId: 267694761
diff --git a/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java b/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
index f012e05..0080e1a 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
@@ -26,18 +26,17 @@
 import static com.google.devtools.build.lib.packages.BuildType.OUTPUT;
 import static com.google.devtools.build.lib.packages.BuildType.OUTPUT_LIST;
 import static com.google.devtools.build.lib.packages.BuildType.TRISTATE;
-import static com.google.devtools.build.lib.syntax.Type.BOOLEAN;
-import static com.google.devtools.build.lib.syntax.Type.INTEGER;
-import static com.google.devtools.build.lib.syntax.Type.INTEGER_LIST;
-import static com.google.devtools.build.lib.syntax.Type.STRING;
-import static com.google.devtools.build.lib.syntax.Type.STRING_DICT;
-import static com.google.devtools.build.lib.syntax.Type.STRING_LIST;
-import static com.google.devtools.build.lib.syntax.Type.STRING_LIST_DICT;
+import static com.google.devtools.build.lib.packages.Type.BOOLEAN;
+import static com.google.devtools.build.lib.packages.Type.INTEGER;
+import static com.google.devtools.build.lib.packages.Type.INTEGER_LIST;
+import static com.google.devtools.build.lib.packages.Type.STRING;
+import static com.google.devtools.build.lib.packages.Type.STRING_DICT;
+import static com.google.devtools.build.lib.packages.Type.STRING_LIST;
+import static com.google.devtools.build.lib.packages.Type.STRING_LIST_DICT;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.query2.proto.proto2api.Build.Attribute.Discriminator;
-import com.google.devtools.build.lib.syntax.Type;
 
 /** Shared code used in proto buffer output for rules and rule classes. */
 public class ProtoUtils {