Add the missing sr-Latn into png files and rename the png locale header

Switch the locale header in the png files from Locale.toString() to
Locale.toLanguageTag(). For example, en_US --> en-us and sr__#Latn
--> sr-Latn. Also clean up recovery a bit to expect the new locale
format.

Bug: 35215015
Test: sr-Latn shows correctly under graphic tests && recovery tests pass
Change-Id: Ic62bab7756cdc6e5f98f26076f7c2dd046f811db
diff --git a/tests/unit/locale_test.cpp b/tests/unit/locale_test.cpp
index f732350..cdaba0e 100644
--- a/tests/unit/locale_test.cpp
+++ b/tests/unit/locale_test.cpp
@@ -19,14 +19,15 @@
 #include "minui/minui.h"
 
 TEST(LocaleTest, Misc) {
-    EXPECT_TRUE(matches_locale("zh_CN", "zh_CN_#Hans"));
-    EXPECT_TRUE(matches_locale("zh", "zh_CN_#Hans"));
-    EXPECT_FALSE(matches_locale("zh_HK", "zh_CN_#Hans"));
-    EXPECT_TRUE(matches_locale("en_GB", "en_GB"));
-    EXPECT_TRUE(matches_locale("en", "en_GB"));
-    EXPECT_FALSE(matches_locale("en_GB", "en"));
-    EXPECT_FALSE(matches_locale("en_GB", "en_US"));
-    EXPECT_FALSE(matches_locale("en_US", ""));
-    // Empty locale prefix in the PNG file will match the input locale.
-    EXPECT_TRUE(matches_locale("", "en_US"));
+  EXPECT_TRUE(matches_locale("zh-CN", "zh-Hans-CN"));
+  EXPECT_TRUE(matches_locale("zh", "zh-Hans-CN"));
+  EXPECT_FALSE(matches_locale("zh-HK", "zh-Hans-CN"));
+  EXPECT_TRUE(matches_locale("en-GB", "en-GB"));
+  EXPECT_TRUE(matches_locale("en", "en-GB"));
+  EXPECT_FALSE(matches_locale("en-GB", "en"));
+  EXPECT_FALSE(matches_locale("en-GB", "en-US"));
+  EXPECT_FALSE(matches_locale("en-US", ""));
+  // Empty locale prefix in the PNG file will match the input locale.
+  EXPECT_TRUE(matches_locale("", "en-US"));
+  EXPECT_TRUE(matches_locale("sr-Latn", "sr-Latn-BA"));
 }