Desktop: Text clipboard support (#3461)

* gray background for viewport texture

* cust copy paste support

* connect clipboard read on web

* fix eyedropper bounds

* cleanup

* add missing char events for some named keys like enter

editor/src/messages/clipboard/mod.rs

@@ -0,0 +1,8 @@
+mod clipboard_message;
+pub mod clipboard_message_handler;
+pub mod utility_types;
+
+#[doc(inline)]
+pub use clipboard_message::{ClipboardMessage, ClipboardMessageDiscriminant};
+#[doc(inline)]
+pub use clipboard_message_handler::ClipboardMessageHandler;