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/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index e23e491..8ca63fc 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
@@ -17,7 +17,7 @@
 import static com.google.devtools.build.lib.packages.Attribute.ANY_RULE;
 import static com.google.devtools.build.lib.packages.Attribute.attr;
 import static com.google.devtools.build.lib.packages.BuildType.LABEL_LIST;
-import static com.google.devtools.build.lib.syntax.Type.BOOLEAN;
+import static com.google.devtools.build.lib.packages.Type.BOOLEAN;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Function;
@@ -52,6 +52,7 @@
 import com.google.devtools.build.lib.packages.RuleClass.Builder.RuleClassType;
 import com.google.devtools.build.lib.packages.RuleClass.Builder.ThirdPartyLicenseExistencePolicy;
 import com.google.devtools.build.lib.packages.RuleFactory.AttributeValues;
+import com.google.devtools.build.lib.packages.Type.ConversionException;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec.VisibleForSerialization;
 import com.google.devtools.build.lib.syntax.Argument;
@@ -60,8 +61,6 @@
 import com.google.devtools.build.lib.syntax.FuncallExpression;
 import com.google.devtools.build.lib.syntax.Runtime;
 import com.google.devtools.build.lib.syntax.SkylarkList;
-import com.google.devtools.build.lib.syntax.Type;
-import com.google.devtools.build.lib.syntax.Type.ConversionException;
 import com.google.devtools.build.lib.util.FileTypeSet;
 import com.google.devtools.build.lib.util.StringUtil;
 import com.google.devtools.build.lib.vfs.PathFragment;