AWT: Conversion from string literal loses const qualifier

Compiling OpenJDK with Visual Studio 2019 and with -Zc:strictStrings flag enabled produces a few compilation errors.

String literal to non-const pointer conversion, when used incorrectly, may result in runtime errors. Using Zc:strictStrings forces users to either use const pointers, or use explicit conversion, which is easier to spot and review.

GCC and Clang already warn on this conversion in all C++ code.