FIX: Toggling a breakpoint by clicking on the linenumber in debugger not possible

[jonasPoehler]

This is a regression introduced through #1343.
With that pull request getModifiers() was switched to getModifiersEx(). However these two methods are not as easily interchangeable (especially when using the mouse-release-event) as it might seem from the deprecation notice. In this particular case the MouseEvent is checked on mouseRelease. However when looking at the documentation of getModifiersEx() (e.g. https://github.com/openjdk/jdk/blob/dfacda488bfbe2e11e8d607a6d08527710286982/src/java.desktop/share/classes/java/awt/event/InputEvent.java#L506C10-L506C10) it gets clear that at that stage, we cannot detect the button click with the help of the modifiers. I did some debugging and at the point of button release getModifiersEx() just returns 0, meaning that no bit is set at all. A possible solution to this is to check which button triggered the release-event with the use of getButton() like I did here. This behaviour was also discovered by someone on stackoverflow a while back: https://stackoverflow.com/questions/60518621/mouseevent-getmodifiersex-call-does-not-work-as-expected-or-as-documented.
Note: The PR #1343 touched another spot where getModifiers() was replaced. Since I am fairly new to this project, I was not sure if the changed code is correct at this point either: https://github.com/mozilla/rhino/pull/1343/files#diff-5d4e8db22e19b87ef92bbee2473a342f75f2e166ff04d18e07cbc02e46c91514L2477. I only noticed that the enclosing method seemingly is never used, so I can't say where the MouseEvent is coming from hence I am unable to tell if that code has to be changed as well.

[gbrail]

Thanks a ton for finding and fixing this!

Since there are additional regressions introduced in #1343, I'm going to:

1. Close this PR
2. Add your commit to a new PR: Fix regressions introduced to debugger #1369
3. If everything works out, merge them together and not squash so that you are in the commit history

Thanks for contributing and please test out the other PR!