LibWeb: Implement implicit submission of HTMLFormElement

Author: https://github.com/trflynn89
Commit: 5d1657f57f
Pull-request: https://github.com/SerenityOS/serenity/pull/23032
Issue: https://github.com/SerenityOS/serenity/issues/22537
Issue: https://github.com/SerenityOS/serenity/issues/22705
Issue: https://github.com/SerenityOS/serenity/issues/23008
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/Lubrsi

Tests/LibWeb/Text/expected/HTML/form-implicit-submission.txt

@@ -0,0 +1,28 @@
+ wfh :^) PASS   wfh :^)    wfh :^) FAIL PASS FAIL   wfh :^) FAIL FAIL PASS  PASS  wfh :^)   wfh :^)  PASS  PASSwfh :^) FAIL   wfh :^) FAIL   wfh :^)   wfh :^) FAIL   wfh :^)    wfh :^)     defaultButton: click button=PASS
+defaultButton: submit
+defaultButton: handledEvent=true
+defaultButtonAsInput: click button=PASS
+defaultButtonAsInput: submit
+defaultButtonAsInput: handledEvent=true
+defaultButtonIsSecond: click button=PASS
+defaultButtonIsSecond: submit
+defaultButtonIsSecond: handledEvent=true
+defaultButtonIsLast: click button=PASS
+defaultButtonIsLast: submit
+defaultButtonIsLast: handledEvent=true
+defaultButtonIsBeforeForm: click button=PASS
+defaultButtonIsBeforeForm: submit
+defaultButtonIsBeforeForm: handledEvent=true
+defaultButtonIsAfterForm: click button=PASS
+defaultButtonIsAfterForm: submit
+defaultButtonIsAfterForm: handledEvent=true
+defaultButtonIsDynamicallyInserted: click button=PASS
+defaultButtonIsDynamicallyInserted: submit
+defaultButtonIsDynamicallyInserted: handledEvent=true
+defaultButtonIsDisabled: handledEvent=false
+noButton: submit
+noButton: handledEvent=true
+noDefaultButton: submit
+noDefaultButton: handledEvent=true
+excessiveBlockingElements1: handledEvent=false
+excessiveBlockingElements2: handledEvent=false