Support optional parameter default expressions that reference instance members of the declaring method's class

[rsmckinney]

Support optional parameter default expressions that reference instance members of the declaring method's class.

class MyClass {
    MyClass(String str = bar()) {. . .} 
    void foo(String str = bar()) {. . .}
    String bar() {. . .}
}

This change will support a couple of efforts planned for the near future.

1. Record copy() feature: Use manifold's optional parameters to make records nicely copyable #698
2. Struct class feature: Provide a "record" class equivalent using properties (manifold-props) #257

Note, the changes required to support this will likely break compiled references to existing optional parameter methods, but being that manifold-params is an experimental project, hopefully this should not come as a surprise.

[rsmckinney]

Support available with release 2025.1.12