Add a "base" set of tracks and assemblies for the embedded demos

[cmdcolin]

• Adds a "base" tracks.ts and assembly.ts that is copied to each embedded demo by a shell script (symlink is not used because i want people to be able to clone this subdirectory and work with it standalone)

• Renames folder demos->embedded_demos

• Removes unused test files in embedded demos

• Gives license:MIT in each demo

• Updates to nextjs 13 in lgv demo (previously had a bug with their swc minfier and @gmod/binary-parser, helped them to get this fixed)

[codecov]

Codecov Report

Merging #3413 (20da5a8) into main (7e93ce7) will not change coverage.
The diff coverage is n/a.

❗ Current head 20da5a8 differs from pull request most recent head 1903f4b. Consider uploading reports for the commit 1903f4b to get more accurate results

@@           Coverage Diff           @@
##             main    #3413   +/-   ##
=======================================
  Coverage   61.23%   61.23%           
=======================================
  Files         816      816           
  Lines       29520    29520           
  Branches     7109     7109           
=======================================
  Hits        18077    18077           
  Misses      11270    11270           
  Partials      173      173           

Impacted Files	Coverage Δ
products/jbrowse-web/src/util.ts	48.33% <0.00%> (ø)

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