Default output_jar_creator to bazel in apk_packaging.bzl.

In CL 959227250, output_jar_creator was defaulted to "bazel" in
rules/java.bzl:singlejar, and removed from rules/android_binary/impl.bzl.
However, rules/apk_packaging.bzl still defaulted output_jar_creator = ""
in _process() and output_jar_creator = None in _build_apk(), and forwarded
the argument to java.singlejar().

Because rules/java.bzl checks `if output_jar_creator:`, passing "" or None
caused the "bazel" default to be bypassed for base module packaging,
producing "Created-By: singlejar" (48 bytes). Feature modules, which call
java.singlejar() directly, picked up "Created-By: bazel" (44 bytes),
triggering Bundletool EntryClashValidator InvalidBundleException.

Defaulting output_jar_creator = "bazel" in both _process() and _build_apk()
ensures consistent 44-byte MANIFEST.MF headers across all module splits.

PiperOrigin-RevId: 967283865
Change-Id: I3bfe26031f086a23cd2912bc07e2452604668952

rules/apk_packaging.bzl

diff --git a/rules/apk_packaging.bzl b/rules/apk_packaging.bzl
index e772207..7fe1896 100644
--- a/rules/apk_packaging.bzl
+++ b/rules/apk_packaging.bzl
@@ -63,7 +63,7 @@
         java_resources_zip = None,
         compress_java_resources = True,
         nocompress_extensions = [],
-        output_jar_creator = "",
+        output_jar_creator = "bazel",
         signing_keys = [],
         signing_lineage = None,
         signing_key_rotation_min_sdk = None,
@@ -207,7 +207,7 @@
         java_resources_zip = None,
         compress_java_resources = False,
         nocompress_extensions = [],
-        output_jar_creator = None,
+        output_jar_creator = "bazel",
         resource_extractor = None,
         toolchain_type = None,
         java_toolchain = None):