String formatting overhaul: Parsing of std::format strings

C++20 adds std::format to the STL as a type-safe and more flexible
alternative to printf and IO streams. fly::BasicString::format was also
an alternative, but used a very tiny subset of printf-styled formatting
strings.

This adds (nearly) fully compliant parsing of the new std::format style
of strings. This style is not used by BasicString yet. Unsupported
features include nested replacement fields and a type analogous to
std::formatter (rather, the ostream<< operator is still used).

Unlike std::format, this implementation supports all character types
(not just char- and wchar_t-based strings). This implementation also
supports full validation of the format string at compile time with
compilers that support consteval. Other compilers will drop invalid
format strings at runtime.

Author: trflynn89

build/win/libfly/libfly.vcxproj

@@ -222,6 +222,7 @@
     <ClInclude Include="..\..\..\fly\types\string\detail\string_classifier.hpp" />
     <ClInclude Include="..\..\..\fly\types\string\detail\string_converter.hpp" />
     <ClInclude Include="..\..\..\fly\types\string\detail\string_formatter.hpp" />
+    <ClInclude Include="..\..\..\fly\types\string\detail\string_formatter_types.hpp" />
     <ClInclude Include="..\..\..\fly\types\string\detail\string_lexer.hpp" />
     <ClInclude Include="..\..\..\fly\types\string\detail\string_streamer.hpp" />
     <ClInclude Include="..\..\..\fly\types\string\detail\string_streamer_traits.hpp" />

build/win/libfly/libfly.vcxproj.filters

@@ -277,6 +277,9 @@
     <ClInclude Include="..\..\..\fly\types\string\detail\string_formatter.hpp">
       <Filter>types\string\detail</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\..\fly\types\string\detail\string_formatter_types.hpp">
+      <Filter>types\string\detail</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\..\fly\types\string\detail\string_lexer.hpp">
       <Filter>types\string\detail</Filter>
     </ClInclude>

build/win/libfly_unit_tests/libfly_unit_tests.vcxproj

@@ -246,6 +246,7 @@
     <ClCompile Include="..\..\..\test\types\string_classifier.cpp" />
     <ClCompile Include="..\..\..\test\types\string_converter.cpp" />
     <ClCompile Include="..\..\..\test\types\string_formatter.cpp" />
+    <ClCompile Include="..\..\..\test\types\string_formatter_types.cpp" />
     <ClCompile Include="..\..\..\test\types\string_lexer.cpp" />
     <ClCompile Include="..\..\..\test\types\string_traits.cpp" />
     <ClCompile Include="..\..\..\test\types\string_unicode.cpp" />

build/win/libfly_unit_tests/libfly_unit_tests.vcxproj.filters

@@ -137,6 +137,9 @@
     <ClCompile Include="..\..\..\test\types\string_formatter.cpp">
       <Filter>types</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\test\types\string_formatter_types.cpp">
+      <Filter>types</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\test\types\string_lexer.cpp">
       <Filter>types</Filter>
     </ClCompile>