fix(build) Redo code coverage reporting, remove istanbul-combine

[jeromesimeon]

Signed-off-by: jeromesimeon jeromesimeon@me.com

Description

Some recent builds are failing due to issues merging code coverage reporting. See e.g., https://github.com/accordproject/markdown-transform/runs/3924510479?check_suite_focus=true

In addition, istanbul-combine is not maintained and has known vulnerabilities.

So I'm finally biting that bullet and re-doing the final code coverage reporting.

This is more painful than expected. One option would be to do a matrix for coveralls in the Github Actions and let coveralls do the merge.

The option chosen here instead is to re-do the code coverage merge using:

1. a script to copy the files into ./coverage
2. use the native nyc merge

Changes

• Remove instanbul-* packages not maintained, failing and with vulnerabilities
• Add scripts for code coverage merge to replace those
• Upgrade nyc NOT upgrading nyc since it doesn't work with coveralls anymore see Coverage paths are no longer fully resolved istanbuljs/istanbuljs#529

Flags

• Still has to be tested live with the coveralls Github Actions app
• If working, this change should be made to all repos

[coveralls]

Coverage decreased (-0.4%) to 85.525% when pulling fcfdeff on jeromesimeon:js-fix-coverage into bc167f9 on accordproject:master.