Make `PileupBuilder.includeMapPositionsOutsideFrInsert` intuitively correct

[clintval]

Closes #980

[clintval]

@jrm5100 could I get your 👀 on this one?

Discussion in this thread: https://github.com/fulcrumgenomics/fgbio/issues/980

[clintval]

We've settled on how the filter is supposed to work and I've updated the documentation.

The filter should now be more obvious in how it is supposed to be used.

No functional change will occur when this PR is merged. The only updates:

• A variable name was updated to be logically correct
• An additional unit test was added for sanity sake
• Better documentation exists for the filter's intended use case

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.62%. Comparing base (3a74fd2) to head (c02e0b3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #981 +/- ## ======================================= Coverage 95.62% 95.62% ======================================= Files 126 126 Lines 7364 7364 Branches 506 500 -6 ======================================= Hits 7042 7042 Misses 322 322 ``` | [Flag](https://app.codecov.io/gh/fulcrumgenomics/fgbio/pull/981/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/fulcrumgenomics/fgbio/pull/981/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics) | `95.62% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics#carryforward-flags-in-the-pull-request-comment) to find out more.

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