Auto merge of #11225 - izgzhen:patch-input-element-file, r=Manishearth

Implement file related functionalities in htmlinputelement and related

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy --faster` does not report any errors
- [x] These changes is related to #11131
- [x] These changes do not require tests because it is a partial implementation

1. Improve the `filemanager_thread` by adding type string and create `SelectedFile`
2. Fill several gaps in `htmlinputelement` implementation related to file type
3. Improve the `File` interface to accommodate the above changes
4. Integrate changes introduced by PR #11189

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11225)
<!-- Reviewable:end -->

components/script/dom/window.rs

@@ -1603,4 +1603,3 @@ fn debug_reflow_events(id: PipelineId, goal: &ReflowGoal, query_type: &ReflowQue
     println!("{}", debug_msg);
 }
 
-no_jsmanaged_fields!(ResourceThreads);