Auto merge of #20327 - kwonoj:fix-ignore, r=paulrouget

fix(keyevent): do not emit default ignorable codepoint

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This PR intends to update `KeyEvent` emit behavior around #18130. Issue https://github.com/servo/servo/issues/17146#issue-233361568 briefly explains what's happening in servo currently - there are KeyboardInput event emitted for separated key (modifier, and `V` in case of paste) and there are also `ReceivedCharacter` event corresponds to `\u{0016}`.

`0x0016` is unicode representation of `Synchronous Idle` (https://en.wikipedia.org/wiki/Synchronous_Idle), belong under category of `Default Ignorable` charater in unicode range doesn't have visual representation (http://www.unicode.org/L2/L2002/02368-default-ignorable.pdf). Currently servo forwards all of emitted event from `winit` including this, eventually leads into double execution of control event.

In this change try to omit default ignorable charater , if given char received is within range of ignorable do not dispatch `KeyEvent`. Once those are omitted, current event handling logic already takes care of key event with correct modifier state so duplicated event handling won't occur.

For implementation perspective, `std::char` in Rust doesn't seem to support `isIdentifierIgnorable` like other platform does (i.e: https://msdn.microsoft.com/en-us/library/aa285330(v=vs.60).aspx / https://docs.oracle.com/javase/7/docs/api/java/lang/Character.html) - so does quick, naïve range comparison check based on unicode range specified in spec, similar to halfbuzz and other does. (https://github.com/harfbuzz/harfbuzz/blob/master/src/hb-unicode-private.hh#L134)

Lastly, this is indeed behavior of `winit` to emit all characters by default. *Why not try to make upstream changes instead?* While I've been reading through issues in `winit`, issue like https://github.com/tomaka/winit/issues/350 trying to emit ignorable character by its intention (delete key `ReceivedCharacter` is also under category of default ignorable) and let each consumer application handles it as needed. I assume it'll cause breaking changes in winit's design if it intends to omit those characters, instead tried to make application-level changes.

Couple of consideration for review

- Is it desired changes to not emit `KeyEvent` for default ignorable chars? Do we rather want mapping / or restoring back to original char as @paulrouget mentioned in https://github.com/servo/servo/issues/17146#issue-233361568?
- Any better, recommended approach to detect unicode char range?
- Maybe try to make upstream changes to `winit` still, like having configuratble way to opt-in(out) those char event?

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #18130 (github issue number if applicable).

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- This PR has been locally tested on Windows, Linux machines.

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ports/servo/glutin_app/window.rs

@@ -346,8 +346,32 @@ impl Window {
         GlRequest::Specific(Api::OpenGlEs, (3, 0))
     }
 
+    /// Detect if given char is default ignorable in unicode
+    /// http://www.unicode.org/L2/L2002/02368-default-ignorable.pdf
+    fn is_identifier_ignorable(&self, ch: &char) -> bool {
+        match *ch {
+            '\u{0000}'...'\u{0008}' | '\u{000E}'...'\u{001F}' |
+            '\u{007F}'...'\u{0084}' | '\u{0086}'...'\u{009F}' |
+            '\u{06DD}' | '\u{070F}' |
+            '\u{180B}'...'\u{180D}' | '\u{180E}' |
+            '\u{200C}'...'\u{200F}' |
+            '\u{202A}'...'\u{202E}' | '\u{2060}'...'\u{2063}' |
+            '\u{2064}'...'\u{2069}' | '\u{206A}'...'\u{206F}' |
+            '\u{FE00}'...'\u{FE0F}' | '\u{FEFF}' |
+            '\u{FFF0}'...'\u{FFF8}' | '\u{FFF9}'...'\u{FFFB}' |
+            '\u{1D173}'...'\u{1D17A}' | '\u{E0000}' |
+            '\u{E0001}' |
+            '\u{E0002}'...'\u{E001F}' | '\u{E0020}'...'\u{E007F}' |
+            '\u{E0080}'...'\u{E0FFF}' => true,
+            _ => false
+        }
+    }
+
     fn handle_received_character(&self, ch: char) {
         let modifiers = Window::glutin_mods_to_script_mods(self.key_modifiers.get());
+        if self.is_identifier_ignorable(&ch) {
+            return
+        }
         if let Some(last_pressed_key) = self.last_pressed_key.get() {
             let event = WindowEvent::KeyEvent(Some(ch), last_pressed_key, KeyState::Pressed, modifiers);
             self.event_queue.borrow_mut().push(event);