Add requestidlecallback ponyfill in @jbrowse/core/util

[cmdcolin]

Added a really basic rIC ponyfill that performs setTimeout(cb,1) for @jbrowse/core/util, used it throughout the codebase where needed

The alternative I can think of is adding the requestidlecallback-polyfill to jbrowse-react-linear-genome-view specifically but probably just better to do this
https://github.com/GMOD/jbrowse-components/tree/ric_polyfill

For compatibility with Safari mostly

Fixes #1659

[codecov]

Codecov Report

Merging #1762 (03319bb) into master (6f27b40) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master    #1762   +/-   ##
=======================================
  Coverage   58.74%   58.74%           
=======================================
  Files         455      455           
  Lines       21033    21038    +5     
  Branches     4979     4983    +4     
=======================================
+ Hits        12355    12358    +3     
- Misses       8368     8370    +2     
  Partials      310      310           

Impacted Files	Coverage Δ
packages/core/util/index.ts	82.42% <75.00%> (+0.22%)	⬆️
...BaseChordDisplay/components/RpcRenderedSvgGroup.js	93.75% <100.00%> (+0.20%)	⬆️
...ins/dotplot-view/src/ServerSideRenderedContent.tsx	84.21% <100.00%> (ø)
...arDisplay/components/ServerSideRenderedContent.tsx	90.00% <100.00%> (ø)
...inearGenomeView/components/RefNameAutocomplete.tsx	89.36% <0.00%> (-4.26%)	⬇️

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