[libc++][test] Move format.functions ASCII tests to libcxx/test/libcxx (#78661)

As @cpplearner explained in microsoft/STL#4328:

> libc++'s "ascii" mode (controlled by the `_LIBCPP_HAS_NO_UNICODE`
> macro) means "every code unit outside ASCII is treated as a valid
> printable character". AFAIK we \[MSVC's STL\] don't support such a mode.

Because these files are testing a non-Standard mode, they should be
moved from `libcxx/test/std` to `libcxx/test/libcxx`.

Author: StephanTLavavej

libcxx/test/std/utilities/format/format.functions/ascii.pass.cpp renamed to libcxx/test/libcxx/utilities/format/format.functions/ascii.pass.cpp

@@ -226,7 +226,7 @@ void test_char() {
     static_assert(sizeof(CharT) == 4, "add support for unexpected size");
     // Unicode fitting in a 32-bit wchar_t
 
-    constexpr wchar_t x  = 0x1ffff;
+    constexpr wchar_t x       = 0x1ffff;
     constexpr std::uint32_t y = 0x1ffff;
     static_assert(x == y);