Update project configuration and snapshot files

- Changed the default project file from `plugin.project.json` to `plugin.project.json5` in `build.rs`.
- Added new project configuration files in JSON5 format for various test cases, including `default.project.json5`, `client_in_folder`, `csv_bug_145`, and others.
- Updated snapshot files to reflect changes in instance structure and properties, ensuring consistency with the new project configurations.
- Removed unnecessary script and module instances from snapshot files to streamline the testing process.

rojo-test/build-tests/optional/default.project.json5

@@ -0,0 +1,15 @@
+{
+  "name": "optional",
+  "tree": {
+    "$className": "Folder",
+    "foo-required": {
+      "$path": "foo.txt"
+    },
+    "foo-optional":{
+      "$path": { "optional": "foo.txt" }
+    },
+    "bar-optional":{
+      "$path": { "optional": "bar.txt" }
+    }
+  }
+}