x/tools/cmd/godoc: "const" declarations with type on right are not grouped with the type

[bcmills]

Run the godoc tool on a file such as https://play.golang.org/p/fnp9JT3Ki_.

The constants with types on the left of "=" are grouped with the type.  The
equivalent constants with types on the right are not.

Since the two styles of declaration produce equivalent constants, they should arguably
also produce equivalent documentation.

[ianlancetaylor]

Comment 1:

Labels changed: added repo-tools, release-none.

[griesemer]

Comment 2:

Types are trivially recognizable in declarations of the form
const c T = x
That is not the case in general for declarations of the form
const c = x
(note that x may have a type).
We can probably use a heuristic to handle cases like
const c = T(x)
but the general case requires type-checking the package.

[bcmills]

Comment 3:

Even just the T(x) case would be a significant improvement.

[bcmills]

Comment 4:

(Also the related T{x} case if T is a struct type.)