feat(window-state): support using a custom filename (#1138)

* feat(window-state): support using a custom filename

ref: https://github.com/tauri-apps/plugins-workspace/pull/1079

* generate api

* fmt

.changes/window-state-custom-filename.md

@@ -0,0 +1,6 @@
+---
+"window-state": "patch"
+"window-state-js": "patch"
+---
+
+Add `Builder::with_filename` to support using a custom filename. Also add `AppHandleExt::file_name` and a similar function in JS, to retrieve it later.

.changes/window-state-default-filename.md

@@ -0,0 +1,5 @@
+---
+"window-state": "patch"
+---
+
+**Breaking change**: Renamed `STATE_FILENAME` const to `DEFAULT_FILENAME`.