Fix Java codegen: map Hack 'mixed' type to 'Object'

Summary:
The Maven build was failing with 'cannot find symbol: class mixed' in
ProductFeedUploadGet.java at 6 locations (fields/getters/setters for
end_time and start_time). 'mixed' is a Hack/PHP type meaning 'any
type'; it is not a valid Java type, so it leaked verbatim from the
API spec into the generated Java source.

Root cause:
- codegen/api_specs/specs/ProductFeedUploadGet.json declares
  end_time and start_time with 'type': 'mixed'.
- CodeGenLanguageJava.js had no mapping for 'mixed', so the type was
  emitted as-is.

Changes:
- codegen/lib/processors/CodeGenLanguageJava.js: add a mapping
  'mixed' -> 'Object' (Java's equivalent of 'any type') so future
  regenerations produce valid Java for any spec field typed 'mixed'.
- sdk/servers/java/release/.../ProductFeedUploadGet.java: replace
  the 6 occurrences of 'mixed' with 'Object' to unblock the build
  without re-running the full codegen.

Note: The 'mixed' references in AdReportRun.java and AdsInsights.java
are enum *value strings* ("mixed"), not types, so they are not
affected and compile correctly.

Reviewed By: jdholstein

Differential Revision: D107971413

fbshipit-source-id: 0b76a9ccc3792585c03f84cc92b0a06088ac4277

Author: satwikareddy3

src/main/java/com/facebook/ads/sdk/ProductFeedUploadGet.java

@@ -42,7 +42,7 @@
  */
 public class ProductFeedUploadGet extends APINode {
   @SerializedName("end_time")
-  private mixed mEndTime = null;
+  private Object mEndTime = null;
   @SerializedName("error_count")
   private Long mErrorCount = null;
   @SerializedName("error_report")
@@ -66,7 +66,7 @@ public class ProductFeedUploadGet extends APINode {
   @SerializedName("progresses")
   private Object mProgresses = null;
   @SerializedName("start_time")
-  private mixed mStartTime = null;
+  private Object mStartTime = null;
   @SerializedName("upload_complete")
   private Boolean mUploadComplete = null;
   @SerializedName("url")
@@ -224,11 +224,11 @@ public String toString() {
   }
 
 
-  public mixed getFieldEndTime() {
+  public Object getFieldEndTime() {
     return mEndTime;
   }
 
-  public ProductFeedUploadGet setFieldEndTime(mixed value) {
+  public ProductFeedUploadGet setFieldEndTime(Object value) {
     this.mEndTime = value;
     return this;
   }
@@ -332,11 +332,11 @@ public ProductFeedUploadGet setFieldProgresses(Object value) {
     return this;
   }
 
-  public mixed getFieldStartTime() {
+  public Object getFieldStartTime() {
     return mStartTime;
   }
 
-  public ProductFeedUploadGet setFieldStartTime(mixed value) {
+  public ProductFeedUploadGet setFieldStartTime(Object value) {
     this.mStartTime = value;
     return this;
   }