Definition items

[tmat]

[Recommended review strategy is commit by commit.]

First commit refactors DefinitionItem and related types.
Second commit adds nullability annotations.
Third commit adds tests for existing behavior of classified DefinitionItem construction from a symbol.
Further commits replace OriginationParts with MetadataLocations array, which contains displayable information for each metadata assembly the symbol occurs in. DefinitionItem can now have both source spans and metadata locations. This allows us to better represent namespaces that span source and metadata.

The change also improves display of metadata locations in Find Results (outputs of GTD, GTB, GTI and FAR).

Before

After

Source namespaces

namespace N
{
    class F
    {
        N.F f;
        global::N.F g;
    }
}

namespace N
{
}

Before:

FAR:

GTD:

After:

FAR:

GTD:

Navigation

Fixes navigation for DefinitionItemEntry items representing symbols whose location may not exist on disk.

[CyrusNajmabadi]

Close to signing off. Have a few questions i'd like info on. overall this seems totally ok :)

[333fred]

Compiler changes LGTM

Behavior was updated to improve consistency with prior releases