Fix packaging of portable data for icu, gdal, and proj

[springmeyer]

Context

We moved to using mason for dependencies in #738. Mason supports the mason link command which places symlinks of files at predictable paths. The build then copies these over into lib/binding when packaging the portable node-mapnik binaries.

The bug

The symlinks were being copied rather than the actual files. This meant that, once published, the data was missing since the symlinks were "broken" (point to non existent data).

Solution

We need to ensure this bug never happens. So this PR moves to removing the mason_packages folder before running the node-mapnik tests. This replicates the point to non existent data situation during node-mapnik travis builds.

This PR also starts passing the -L flag to cp to deference the symlinks during copy to ensure we are copying the full data and not just the symlink.

[codecov-io]

Codecov Report

Merging #750 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #750   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files          42       42           
  Lines        8772     8772           
=======================================
  Hits         8442     8442           
  Misses        330      330

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