Fix coping and moving files around using the file tree (#568)

* Implement write/read buffers in electron fill

This makes cutting and copy files from the file tree work.

* Implement fs.createReadStream

This is used by the file tree to copy files.

* Allow passing proxies back from client to server

This makes things like piping streams possible.

* Synchronously bind to proxy events

This eliminates any chance whatsoever of missing events due to binding
too late.

* Make it possible to bind some events on demand

* Add some protocol documentation

packages/ide/src/fill/electron.ts

@@ -171,8 +171,10 @@ const newCreateElement = <K extends keyof HTMLElementTagNameMap>(tagName: K): HT
 document.createElement = newCreateElement;
 
 class Clipboard {
-	public has(): boolean {
-		return false;
+	private readonly buffers = new Map<string, Buffer>();
+
+	public has(format: string): boolean {
+		return this.buffers.has(format);
 	}
 
 	public readFindText(): string {
@@ -190,6 +192,14 @@ class Clipboard {
 	public readText(): Promise<string> {
 		return clipboard.readText();
 	}
+
+	public writeBuffer(format: string, buffer: Buffer): void {
+		this.buffers.set(format, buffer);
+	}
+
+	public readBuffer(format: string): Buffer | undefined {
+		return this.buffers.get(format);
+	}
 }
 
 class Shell {