Doc tool flags missing annotations on variable declarations

[stephanos]

Expected Behavior

Running internal/cmd/build/main.go via go run . check fails if there's a doc comment on a function variable declaration without Exposed as:.

Actual Behavior

It should ignore variable declarations in functions.

Steps to Reproduce the Problem

For example:

// If the priority only contains default values, return nil instead
// - since there's no need to send the default values to the server.
var defaultPriority Priority

See 5ff0c1c