Add integration testing step in CI

[berniegp]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless necessary)
• no

Related issue numbers:

Description

• The build job now outputs an npm package tarball as build artifact
• Moves the multi-platform GitHub action CI tests to a new packageTest job.
• The new job checks
  • that the built package tarball can be installed and used in a minimal integration test
  • that the above works in both commonjs and module package types

This change will allow the build toolchain to use newer tool versions that are not available in all supported node versions of this package. The previous approach built the project on all supported node versions which adds unneeded extra complexity for real uses of this package.