Create datasource for cells to make lazy-loading possible

[benasher44]

Changes in this pull request

Allows non-Array data sources, so that we can lazy-load

Checklist

• [x] All tests pass. Demo project builds and runs.
• [x] I added tests, an experiment, or detailed why my change isn't tested.
• [x] I added an entry to the CHANGELOG.md for any breaking changes, enhancements, or bug fixes.
• [x] I have reviewed the contributing guide

TODO

• [x] Update diffing to only look at on-screen cells

[pg-infosec]

Vulnerable Package: kramdown Affected Range: < 2.3.0 Fixed Version: 2.3.0 Related CVE: CVE-2020-14001 Severity: HIGH

More Information: Please consider upgrading kramdown to prevent deploying vulnerable code into production. For more information, visit: https://nvd.nist.gov/vuln/detail/CVE-2020-14001, or visit the FAQ

[codecov-commenter]

Codecov Report

Merging #186 into master will decrease coverage by 0.28%. The diff coverage is 86.03%.

@@            Coverage Diff             @@
##           master     #186      +/-   ##
==========================================
- Coverage   80.84%   80.56%   -0.28%     
==========================================
  Files          31       33       +2     
  Lines        2082     2227     +145     
==========================================
+ Hits         1683     1794     +111     
- Misses        399      433      +34     

Impacted Files	Coverage Δ
Sources/TableViewDriver.swift	80.00% <42.86%> (-5.90%)	:arrow_down:
Sources/TableCellViewModelDataSource.swift	78.26% <78.26%> (ø)
Sources/Diffing.swift	81.11% <90.20%> (-12.22%)	:arrow_down:
Sources/TableViewModel.swift	94.05% <93.94%> (-1.26%)	:arrow_down:
Tests/TableView/TableViewLazyDiffingTest.swift	97.37% <97.37%> (ø)
Sources/CellContainerViewProtocol.swift	69.57% <100.00%> (ø)
Sources/UITableView+Extensions.swift	100.00% <100.00%> (ø)
Tests/TableView/TableViewDiffingTests.swift	98.72% <100.00%> (ø)
Tests/TableView/TableViewMocks.swift	94.00% <100.00%> (+0.25%)	:arrow_up:
Tests/TableView/TableViewModelTests.swift	100.00% <100.00%> (ø)
... and 3 more