jest-diff: Add firstOrLastEmptyLineReplacement option and export 3 diffLines functions

[pedrottimark]

Summary

1. replace another hard-coded string with an option

2. export diffLinesUnified2 which jest-snapshot will need to ignore indentation

3. delete redundant code to reduce inconsistent behavior

Because diffLines.ts is completely re-written, you might see if Split view is easier to review

Test plan

diffs.test.ts

• added 2 new tests to confirm that default export was inconsistent
• updated 4 tests for empty line to automatically trim space in default export

printDiffOrStringified.test.ts.snap

• updated 1 snapshot for empty line to automatically trim space in default export

[pedrottimark]

Examples for the next pull request reminded me of problems in edge cases because ''.split('\n') returns [''] instead of empty array:

• added splitLines0 as a named export
• refactored diffStringsUnified to call diffLinesUnified for edge cases of all common or no common to make sure that the difference is consistent (for example, the baseline code for all common ignored the expand: false option)

To avoid too much chaos in Changed Files I will leave as a future chore to move diffStringsUnified and diffStringsRaw from the printDiffs.ts file to the diffStrings.ts file, which seems more intuitive

[codecov-io]

Codecov Report

Merging #8955 into master will decrease coverage by 0.22%.
The diff coverage is 96.96%.

@@            Coverage Diff             @@
##           master    #8955      +/-   ##
==========================================
- Coverage    64.2%   63.98%   -0.23%     
==========================================
  Files         276      276              
  Lines       11718    11638      -80     
  Branches     2868     2858      -10     
==========================================
- Hits         7523     7446      -77     
+ Misses       3563     3562       -1     
+ Partials      632      630       -2

Impacted Files	Coverage Δ
packages/jest-diff/src/normalizeDiffOptions.ts	100% <ø> (ø)	⬆️
packages/jest-diff/src/printDiffs.ts	100% <100%> (+2.59%)	⬆️
packages/jest-diff/src/joinAlignedDiffs.ts	100% <100%> (ø)	⬆️
packages/jest-diff/src/diffLines.ts	95.23% <95.12%> (-1.54%)	⬇️
packages/jest-diff/src/index.ts	81.48% <96.15%> (+3.43%)	⬆️

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[jeysal]

Kinda hard to review such a big change, but since the test changes seem ok, the code looks simpler, and there's no red flags, lgtm 😄

[github-actions]

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