Fix zoom to behavior being inaccurate with many displayed regions visible

[cmdcolin]

Fixes #3083

This is a one-liner fix in the LGV model with a couple of fixed tests

Intuitively using the app gives reasonable values for rubberband selections (which are the primary user of the moveTo function that we fix here) even with many displayed regions visible (which commonly occurs with show all regions and synteny views)

https://jbrowse.org/code/jb2/fix_zoomto/?config=test_data%2Fconfig_dotplot.json&session=share-qZrNF9OGYz&password=MMo0X can be tested and appear to work ok

[codecov]

Codecov Report

Merging #3085 (319e1a1) into main (d10927a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #3085   +/-   ##
=======================================
  Coverage   61.34%   61.34%           
=======================================
  Files         594      594           
  Lines       27282    27282           
  Branches     6601     6601           
=======================================
  Hits        16735    16735           
  Misses      10249    10249           
  Partials      298      298           

Impacted Files	Coverage Δ
.../linear-genome-view/src/LinearGenomeView/index.tsx	84.28% <100.00%> (ø)
products/jbrowse-web/src/util.ts	27.27% <0.00%> (ø)

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