As discussed on the mailing list, AbstractDeclarationBuilder::openDeclaration(QualifiedIdentifier) makes little sense semantically. I added an overload taking an Identifier, with the intention of deprecating and removing the QID overload in the future.

This commit makes the QMLJS plugin use the openDeclaration(Identifier) overload everywhere.

Since I made a lot of code use Identifier directly, I had to add a few conversions to QualifiedIdentifier in order to pass it to openContext. Ideally openContext should take an Identifier too, but that's harder to change (I posted a separate thread in the mailing list about it).

Compiled, ran unit tests. A few tests fail due to unrelated problems (could be my local environment), but the failures are exactly the same as without this commit.