Improve visibility of SNPs on alignments track

[cmdcolin]

1. rounds to nearest px to avoid fractional pixels which can blur color
2. use orange instead of amber for G
3. standardize on getContrastText

see '2-way swipes' in the 'files changed' for differences

the amber->orange change increases contrast ratio from 1.09 to 1.44 (amber vs lightgrey -> orange vs lightgrey) according to https://accessibleweb.com/color-contrast-checker/ at possible cost for being closer to red

orange #ff9800
amber #ffc107
lightgrey #d3d3d3

[cmdcolin]

note: its quite difficult to get the contrast very good at all with the orange/yellow on grey but it is the 'traditional' color

[codecov]

Codecov Report

Merging #3534 (629a336) into main (9b8fcc9) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

❗ Current head 629a336 differs from pull request most recent head b74e059. Consider uploading reports for the commit b74e059 to get more accurate results

@@            Coverage Diff             @@
##             main    #3534      +/-   ##
==========================================
- Coverage   62.78%   62.70%   -0.08%     
==========================================
  Files         866      866              
  Lines       30271    30282      +11     
  Branches     7295     7290       -5     
==========================================
- Hits        19006    18989      -17     
- Misses      11076    11104      +28     
  Partials      189      189              

Impacted Files	Coverage Δ
packages/core/ui/theme.ts	72.97% <ø> (ø)
...gins/alignments/src/PileupRenderer/configSchema.ts	50.00% <ø> (ø)
...ns/alignments/src/PileupRenderer/PileupRenderer.ts	52.43% <100.00%> (+0.19%)	⬆️
...nts/src/SNPCoverageRenderer/SNPCoverageRenderer.ts	74.40% <100.00%> (+0.20%)	⬆️

... and 5 files with indirect coverage changes

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[cmdcolin]

doing the "swipe" operation on the updated snapshot tests in this PR also show the evolution

[garrettjstevens]

Agreed, orange has a lot better contrast, and I think it's still sufficiently different from red.

[cmdcolin]

went back to 1px instead of 1.5px as the fractional could be blurry. should still have better contrast now

[cmdcolin]

also standardizes on theme.palette.contrastColor(...) across both SequenceTrack and AlignmentsTrack...was using a custom util function we wrote @jbrowse/core/util/colors -> contrastingTextColor but I think the built in MUI solution is a bit better (chooses black on orange instead of white on orange for example)