Performance improvements on macOS by using Instruments

[zenangst]

• Stop invalidating the FamilyScrollView when the window is set to nil
• Add checks for not doing extra work when the FamilyScrollView is performing batch updates
• Only invalidate the current rectangle when FamilyWrapperView wants to invalidate the FamilyScrollView.

[codecov-io]

Codecov Report

Merging #147 into master will decrease coverage by 0.07%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
- Coverage   83.23%   83.15%   -0.08%     
==========================================
  Files          11       11              
  Lines         859      855       -4     
==========================================
- Hits          715      711       -4     
  Misses        144      144

Flag	Coverage Δ
#iOS	64.51% <ø> (ø)	:arrow_up:
#macOS	83.15% <100%> (-0.08%)	:arrow_down:
#tvOS	64.51% <ø> (ø)	:arrow_up:

Impacted Files	Coverage Δ
Sources/macOS/Classes/FamilyWrapperView.swift	82.19% <100%> (-0.93%)	:arrow_down:

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