Common/FileSystem: Add IsAbsolutePath() and tests

src/common/file_system.h

@@ -137,6 +137,9 @@ void SanitizeFileName(char* Destination, u32 cbDestination, const char* FileName
 void SanitizeFileName(String& Destination, const char* FileName, bool StripSlashes = true);
 void SanitizeFileName(String& Destination, bool StripSlashes = true);
 
+/// Returns true if the specified path is an absolute path (C:\Path on Windows or /path on Unix).
+bool IsAbsolutePath(const std::string_view& path);
+
 /// Replaces the extension of a filename with another.
 std::string ReplaceExtension(std::string_view path, std::string_view new_extension);