Merge default case with other adjacent fall-through cases

[niloc132]

Input source: https://github.com/geogebra/geogebra/blob/3618a4ad1d341d8d155c866e320a223ed2687249/source/shared/common/src/main/java/org/geogebra/common/main/settings/AlgebraStyle.java#L102-L111

Apparently, app.isDesktop() compiles to false, and app.isHTML5Applet() compiles to true. This results in the entire method compiling out as

function Jjj(a) {
    switch (a.A) {
        case 0:
            return !1;
        case 5:
        default:
        case 4:
            return !0;
    }
}

I'm not presently aware of which pass is removing the duplicate return false statements, or why the cases are reordered, but if we removed the case statements that fall through with the default, the existing DCE "only two branches in a switch" optimization would be capable of rewriting to

function Jjj(n) {
    return n.A != 0;
}

[niloc132]

JsDuplicateCaseFolder already combines other case statements (and apparently reorders them?) - we would need to move/copy this to the java optimization loop to expect DCE to rewrite a two-branch switch/case into an if/else.

Moving that code seems a little fraught, it toStrings() statements into strings to use for a key to deduplicate. I'm not sure we have a better way to do it, but #10285 also needs something like that.