[Bug]: PrintTo(char8_t), PrintTo(char16_t) behave incorrectly

[cor3ntin]

Describe the issue

charN_t are cast to char32_t before being displayed using the U+xxxx notation.
This is incorrect for values that do not represent valid codepoints, such as lone surrogates, char8_t values outside the basic Latin1 range, etc.

This was found by a Clang warning to detect incorrect conversions between charN_t that we are rolling out,

Steps to reproduce the problem

https://compiler-explorer.com/z/xE56jbK5M

#include <gtest/gtest-printers.h>
#include <iostream>

int main() {
    testing::internal::PrintTo(char8_t(0x80), 
                                                 &std::cout);
}

What version of GoogleTest are you using?

trunk

What operating system and version are you using?

What compiler and version are you using?

clang trunk

What build system are you using?

Additional context

No response

[zmodem]

@derekmauro can you take a look? This is for

googletest/googletest/include/gtest/gtest-printers.h

Lines 522 to 530 in 5719306

	GTEST_API_ void PrintTo(char32_t c, ::std::ostream* os);
	inline void PrintTo(char16_t c, ::std::ostream* os) {
	PrintTo(ImplicitCast_<char32_t>(c), os);
	}
	#ifdef __cpp_lib_char8_t
	inline void PrintTo(char8_t c, ::std::ostream* os) {
	PrintTo(ImplicitCast_<char32_t>(c), os);
	}
	#endif

[jbulow]

Any progress on this issue?