ICUTimeConversion: Fix buffer overflows and add more error handling.

* Declare databridge buffer lengths in LocaleBackend.
 * Use strcpy instead of strlcpy when writing to databridge buffers
   (this is the first fix for #18598.)
 * Check for overflows and error out when they happen.
 * Verify that ICU actually knows the timezone in question
   and fall back to GMT if it does not (this would also fix that crash.)

Fixes #18598.

headers/private/libroot/locale/LocaleBackend.h

@@ -102,12 +102,14 @@ struct LocaleTimeDataBridge {
 
 
 struct TimeConversionDataBridge {
+	static const int32 		kTZNameLength = 64;
+
 private:
 	int						localDaylight;
 	long					localTimezone;
 	char*					localTZName[2];
-	char					localTZName0[64];
-	char					localTZName1[64];
+	char					localTZName0[kTZNameLength];
+	char					localTZName1[kTZNameLength];
 
 public:
 	int*					addrOfDaylight;