export cmake function for shaderc_compiling

Remove unused add_shader and shaderc
Example usage:
```
shaderc_parse(
  CLI
  ${ARGS_TYPE} ${PLATFORM_I} WERROR
  "$<$<CONFIG:debug>:DEBUG>$<$<CONFIG:relwithdebinfo>:DEBUG>"
  FILE ${SHADER_FILE_ABSOLUTE}
  OUTPUT ${OUTPUT}
  PROFILE ${PROFILE}
  O "$<$<CONFIG:debug>:0>$<$<CONFIG:release>:3>$<$<CONFIG:relwithdebinfo>:3>$<$<CONFIG:minsizerel>:3>"
  VARYINGDEF ${ARGS_VARYING_DEF}
  INCLUDES ${BGFX_SHADER_INCLUDE_PATH}
  BIN2C BIN2C ${SHADER_FILE_NAME_WE}_${PROFILE_EXT}
)
```

CMakeLists.txt

@@ -161,6 +161,8 @@ if( BGFX_INSTALL )
 
 	# install tools
 	if( BGFX_BUILD_TOOLS )
+		install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/cmake/bgfxToolUtils.cmake
+			DESTINATION "${config_install_dir}")
 		install( TARGETS shaderc
 			EXPORT "${TARGETS_EXPORT_NAME}"
 			DESTINATION "${CMAKE_INSTALL_BINDIR}" )