Accept --overlay-name flag in idmap2

To support allowing for multiple <overlay> tags in one package, idmap2
must be able to generate an idmap for an individual <overlay> tag.

`idmap2 create` now accepts a --overlay-name flag that specifies which
tag to use to generate the idmap. The value of --overlay-name should be
set to the value of the android:name attribute on the <overlay> tag to
use.

If the flag is not present, idmap2 will look for an <overlay> tag with
no value for android:name.

Bug: 162841629
Test: libandroidfw_tests
Test: libidmap2_tests
Change-Id: I02316d0b88773f02c04a5d462be9825016fa496d
diff --git a/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp b/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
index c3a3e0b..524aabc 100644
--- a/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
+++ b/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
@@ -33,7 +33,7 @@
 namespace android::idmap2 {
 
 TEST(BinaryStreamVisitorTests, CreateBinaryStreamViaBinaryStreamVisitor) {
-  std::string raw(reinterpret_cast<const char*>(idmap_raw_data), idmap_raw_data_len);
+  std::string raw(reinterpret_cast<const char*>(idmap_raw_data), kIdmapRawDataLen);
   std::istringstream raw_stream(raw);
 
   auto result1 = Idmap::FromBinaryStream(raw_stream);