SF-3240 Fix crashes when a draft book has an invalid book id

[pmachapman]

This PR fixes crashes that occur viewing or applying a draft, when a source book's book id is the wrong case, and the draft was generated from that source.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.78%. Comparing base (2f218f7) to head (6c99906).
Report is 1 commits behind head on master.

Additional details and impacted files

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  Coverage   82.78%   82.78%           
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  Files         563      563           
  Lines       32528    32528           
  Branches     5271     5293   +22     
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  Hits        26929    26929           
+ Misses       4822     4810   -12     
- Partials      777      789   +12     

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[josephmyers]

For testing, I'm going to start the draft, per steps, and let it run overnight.

PR Overview

This PR fixes crashes that occur when a draft book has an invalid book id by ensuring that the correct stylesheet for the book is used during conversion.

• Updated the GetBookText and GetDeltaFromUsfm methods in ParatextService to pass scrText.ScrStylesheet(bookNum) instead of the book number
• Added two new tests to validate the behavior when a variant book id is used in USFM to USX conversions

Reviewed Changes

File	Description
test/SIL.XForge.Scripture.Tests/Services/ParatextServiceTests.cs	Adds tests for override behavior with variant book ids in GetBookText and GetDeltaFromUsfmAsync methods
src/SIL.XForge.Scripture/Services/ParatextService.cs	Updates method calls to use scrText.ScrStylesheet(bookNum) for USFM conversion

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[josephmyers]

This change makes sense, and the draft generated from KJVA can be applied

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @pmachapman)