Support load fixing on struct members (dotexpr) instead of just callexpr (#1972)

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**What type of PR is this?**

> Bug fix

**What package or component does this PR mostly affect?**

> For example:
>
> all

**What does this PR do? Why is it needed?**

The changes introduced by #1164 largely support what I need – automatic
loading of non-rule symbols from known loads – except it only supports
`CallExpr`. For imported struct fields, these are not automatically
picked up, and the ergonomics of getting them loaded in Gazelle has been
tricky for me. I am hoping this is a reasonable fix to this.

**Which issues(s) does this PR fix?**

Fixes #1971 

**Other notes for review**

I haven't written Go in a while so please forgive the mess.