Logging: Add customizable logging backends and fmtlib based macros

* Change the logging backend to support multiple sinks through the
Backend Interface
* Add a new set of logging macros to use fmtlib instead.
* Qt: Compile as GUI application on windows to make the console hidden by
default. Add filter configuration and a button to open log location.
* SDL: Migrate to the new logging macros

src/common/logging/text_formatter.h

@@ -10,22 +10,10 @@ namespace Log {
 
 struct Entry;
 
-/**
- * Attempts to trim an arbitrary prefix from `path`, leaving only the part starting at `root`. It's
- * intended to be used to strip a system-specific build directory from the `__FILE__` macro,
- * leaving only the path relative to the sources root.
- *
- * @param path The input file path as a null-terminated string
- * @param root The name of the root source directory as a null-terminated string. Path up to and
- *             including the last occurrence of this name will be stripped
- * @return A pointer to the same string passed as `path`, but starting at the trimmed portion
- */
-const char* TrimSourcePath(const char* path, const char* root = "src");
-
 /// Formats a log entry into the provided text buffer.
-void FormatLogMessage(const Entry& entry, char* out_text, size_t text_len);
+std::string FormatLogMessage(const Entry& entry);
 /// Formats and prints a log entry to stderr.
 void PrintMessage(const Entry& entry);
 /// Prints the same message as `PrintMessage`, but colored acoording to the severity level.
 void PrintColoredMessage(const Entry& entry);
-}
+} // namespace Log