Fix kitty keyboard "Report event types" behavior not matching spec

According to spec:
- The Enter, Tab and Backspace keys will not have release events unless
  "Report all keys as escape codes" is also set.
- Key events that result in text are reported as plain UTF-8 text, so
  events are not supported for them, unless the application requests
  "key report" mode.

I checked kitty's behavior. While it does report release events for keys
that result in text as CSI sequences, press and repeat events for these
are reported as plain UTF-8 text. This commit changes Xterm.js to match
this behavior.

Author: zeertzjq

src/common/input/KittyKeyboard.test.ts

@@ -453,26 +453,86 @@ describe('KittyKeyboard', () => {
     describe('event types (press/repeat/release)', () => {
       const flags = KittyKeyboardFlags.DISAMBIGUATE_ESCAPE_CODES | KittyKeyboardFlags.REPORT_EVENT_TYPES;
 
-      it('press event (default, no suffix)', () => {
+      it('UTF-8 text press event', () => {
         const result = kitty.evaluate(createEvent({ key: 'a' }), flags, KittyKeyboardEventType.PRESS);
-        assert.strictEqual(result.key, '\x1b[97u');
+        assert.strictEqual(result.key, 'a');
+      });
+
+      it('Escape key press event (default, no suffix)', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Escape' }), flags, KittyKeyboardEventType.PRESS);
+        assert.strictEqual(result.key, '\x1b[27u');
+      });
+
+      it('Enter key press event → legacy \\r', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Enter' }), flags, KittyKeyboardEventType.PRESS);
+        assert.strictEqual(result.key, '\r');
+      });
+
+      it('Tab key press event → legacy \\t', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Tab' }), flags, KittyKeyboardEventType.PRESS);
+        assert.strictEqual(result.key, '\t');
+      });
+
+      it('Backspace key press event → legacy \\x7f', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Backspace' }), flags, KittyKeyboardEventType.PRESS);
+        assert.strictEqual(result.key, '\x7f');
       });
 
       it('press event explicit :1 when modifiers present', () => {
         const result = kitty.evaluate(createEvent({ key: 'a', ctrlKey: true }), flags, KittyKeyboardEventType.PRESS);
         assert.strictEqual(result.key, '\x1b[97;5u');
       });
 
-      it('repeat event → :2 suffix', () => {
+      it('UTF-8 text repeat event', () => {
         const result = kitty.evaluate(createEvent({ key: 'a' }), flags, KittyKeyboardEventType.REPEAT);
-        assert.strictEqual(result.key, '\x1b[97;1:2u');
+        assert.strictEqual(result.key, 'a');
+      });
+
+      it('Escape key repeat event → :2 suffix', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Escape' }), flags, KittyKeyboardEventType.REPEAT);
+        assert.strictEqual(result.key, '\x1b[27;1:2u');
+      });
+
+      it('Enter key repeat event → legacy \\r', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Enter' }), flags, KittyKeyboardEventType.REPEAT);
+        assert.strictEqual(result.key, '\r');
+      });
+
+      it('Tab key repeat event → legacy \\t', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Tab' }), flags, KittyKeyboardEventType.REPEAT);
+        assert.strictEqual(result.key, '\t');
+      });
+
+      it('Backspace key repeat event → legacy \\x7f', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Backspace' }), flags, KittyKeyboardEventType.REPEAT);
+        assert.strictEqual(result.key, '\x7f');
       });
 
       it('release event → :3 suffix', () => {
         const result = kitty.evaluate(createEvent({ key: 'a' }), flags, KittyKeyboardEventType.RELEASE);
         assert.strictEqual(result.key, '\x1b[97;1:3u');
       });
 
+      it('Escape key release event → :3 suffix', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Escape' }), flags, KittyKeyboardEventType.RELEASE);
+        assert.strictEqual(result.key, '\x1b[27;1:3u');
+      });
+
+      it('Enter key release event is not reported', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Enter' }), flags, KittyKeyboardEventType.RELEASE);
+        assert.strictEqual(result.key, undefined);
+      });
+
+      it('Tab key release event is not reported', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Tab' }), flags, KittyKeyboardEventType.RELEASE);
+        assert.strictEqual(result.key, undefined);
+      });
+
+      it('Backspace key release event is not reported', () => {
+        const result = kitty.evaluate(createEvent({ key: 'Backspace' }), flags, KittyKeyboardEventType.RELEASE);
+        assert.strictEqual(result.key, undefined);
+      });
+
       it('release with modifier → mod:3', () => {
         const result = kitty.evaluate(createEvent({ key: 'a', ctrlKey: true }), flags, KittyKeyboardEventType.RELEASE);
         assert.strictEqual(result.key, '\x1b[97;5:3u');

src/common/input/KittyKeyboard.ts

@@ -477,7 +477,12 @@ export class KittyKeyboard {
 
     if (flags & KittyKeyboardFlags.REPORT_ALL_KEYS_AS_ESCAPE_CODES) {
       useCsiU = true;
-    } else if (reportEventTypes) {
+    } else if (reportEventTypes && eventType === KittyKeyboardEventType.RELEASE) {
+      // Per spec, Enter/Tab/Backspace will not have release events unless "Report all keys as
+      // escape codes" (which is handled by the branch above) is also set.
+      if (keyCode === 13 || keyCode === 9 || keyCode === 127) {
+        return result;
+      }
       useCsiU = true;
     } else if (flags & KittyKeyboardFlags.DISAMBIGUATE_ESCAPE_CODES) {
       // Per spec, Enter/Tab/Backspace "still generate the same bytes as in legacy