Incorrect location for undocumented Core methods

For example:

```m2
i1 : locate makeDocumentTag (sin, Number)

o1 = /usr/share/Macaulay2/typicalvalues.m2:271:0

o1 : FilePosition
```
That file doesn't exist! It should be `/usr/share/Macaulay2/Core/typicalvalues.m2`.

I think the problem is that we call `undocumented` on this method in `Core`, but `makeDocumentTag` changes the package to `Macaulay2Doc`, messing up the path.

Reproduce the `locate makeDocumentTag (sin, Number)` example and inspect the `undocumented` handling in `Core`, along with `makeDocumentTag` and `Macaulay2Doc`. Trace how the package changes while generating the location for `Core/typicalvalues.m2`; done means the reported path points to the existing Core file.

Written by the indexing model from the issue text.