apiviewgo hoists const and var values

`const` and `var` values appear literally in API reviews. For example, a `const` like this:
```go
package foo

import "bar"

const Foo = bar.Baz
```
appears in a review like `const Foo = bar.Baz` because `apiviewgo` simply records the value syntax without trying to resolve any reference to another package:
https://github.com/Azure/azure-sdk-tools/blob/c9853b6ba331e01375283037fd0f7cc47f1177b4/src/go/cmd/pkg.go#L128-L131

Reviews would be more informative if `apiviewgo` instead found the value of `bar.Baz` and hoisted it into `foo`.

Start in src/go/cmd/pkg.go around lines 128-131, where apiviewgo records const and var values. Trace how a value such as bar.Baz is represented in the API review and determine how its referenced value could be resolved across packages. Done means referenced values are hoisted into the reviewing package instead of appearing only as the original syntax.

Written by the indexing model from the issue text.