Typescriptify some integration tests

[cmdcolin]

Adds a helper function "createView" that renders the LGV, and gives back a handle to the view with correct typescript types

Also fixes a flaky test on main: it complains the test was torn down but then an async import was made
https://github.com/GMOD/jbrowse-components/runs/7102110874?check_suite_focus=true#step:5:81 which is fixed by not loading an alignments track at all in this test (just using trackRenderingContainer for click and drag)

[codecov]

Codecov Report

Merging #3067 (c15c115) into main (9f87f01) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3067      +/-   ##
==========================================
- Coverage   61.57%   61.56%   -0.02%     
==========================================
  Files         591      591              
  Lines       26977    26986       +9     
  Branches     6529     6529              
==========================================
+ Hits        16611    16613       +2     
- Misses      10069    10076       +7     
  Partials      297      297              

Impacted Files	Coverage Δ
...rc/LinearGenomeView/components/TracksContainer.tsx	63.75% <ø> (ø)
products/jbrowse-web/src/tests/util.tsx	93.84% <100.00%> (+0.98%)	⬆️
...svg/src/SvgFeatureRenderer/components/Segments.tsx	85.71% <0.00%> (-7.15%)	⬇️
...src/SvgFeatureRenderer/components/FeatureLabel.tsx	77.41% <0.00%> (-6.46%)	⬇️
...gins/svg/src/SvgFeatureRenderer/components/util.ts	91.83% <0.00%> (-4.09%)	⬇️
...FeatureRenderer/components/ProcessedTranscript.tsx	87.32% <0.00%> (-1.41%)	⬇️
packages/core/util/layouts/GranularRectLayout.ts	86.86% <0.00%> (-0.43%)	⬇️
products/jbrowse-web/src/util.ts	27.27% <0.00%> (ø)

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