Use static_cast instead of ImplicitCast_ for character conversions

Clang has recently added "warnings when mixing different charN_t types" [1].
The rationale is that "charN_t represent code units of different UTF encodings.
Therefore the values of 2 different charN_t objects do not represent the same
characters."

Note that the warning here may be legitimate - from #4762:
"[...] This is incorrect for values that do not represent valid codepoints."

For the time being, silence the warning by being more explicit about the
conversion being intentional by using static_cast.

Link: llvm/llvm-project#138708 [1]
PiperOrigin-RevId: 760644157
Change-Id: I2e6cc1871975455cecac8731b2f93fd5beeaf0e1

Author: Abseil Team

googletest/include/gtest/gtest-printers.h

@@ -521,11 +521,15 @@ GTEST_API_ void PrintTo(wchar_t wc, ::std::ostream* os);
 
 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);
+  // TODO(b/418738869): Incorrect for values not representing valid codepoints.
+  // Also see https://github.com/google/googletest/issues/4762.
+  PrintTo(static_cast<char32_t>(c), os);
 }
 #ifdef __cpp_lib_char8_t
 inline void PrintTo(char8_t c, ::std::ostream* os) {
-  PrintTo(ImplicitCast_<char32_t>(c), os);
+  // TODO(b/418738869): Incorrect for values not representing valid codepoints.
+  // Also see https://github.com/google/googletest/issues/4762.
+  PrintTo(static_cast<char32_t>(c), os);
 }
 #endif