Incorrect source location in declared-at tags for synthesized equations

[Jesper Öqvist]

With JastAdd 2.3.0, the declared-at comment for a synthesized attribute equation point to the declaration of the attribute, not necessarily the equation.

For example, in ExtendJ the AddExpr.type() equation is declared at java4/frontend/TypeAnalysis.jrag:350:

  eq AddExpr.type() {
    ...
  }

However, the generated declared-at comment for the attribute points to the declaration of Expr.type() at java4/frontend/TypeAnalysis.jrag:295:

  syn lazy TypeDecl Expr.type();

[Jesper Öqvist]

Improve equation documentation comment generation

The documentation comment for an equation is now used in the generated method, instead of the documentation comment for the declaration.

This commit also refactors the emitAttrEquation methods into three separate methods to remove confusing overloading.

fixes #285 (bitbucket)

→ <<cset d31d85622252>>