feat(log): add Builder::split to get the raw logger implementation (#1579)

* feat(log): add Builder::split to get the raw logger implementation

This function lets you split the Builder to return the raw logger implementation along the TauriPlugin to be registered. Useful to pipe the logger to other implementations such as multi_log or tauri-plugin-devtools, allowing the plugin to be used along other logging systems.

* clippy

* covector

.changes/log-split.md

@@ -0,0 +1,5 @@
+---
+"log-plugin": patch
+---
+
+Added `Builder::split` which returns the raw logger implementation so you can pipe to other loggers such as `multi_log` or `tauri-plugin-devtools`.