[Backport 2021.02.xx] #5765, #7617: Update sld and geocss dependencies (#7656)

[allyoucanmap]

Description

This PR updates the geostyler parser using the @geosolutions npm package instead of the reference to the github repository.
Updated libraries:

• geostyler-sld-parser -> @geosolutions/geostyler-sld-parser (include opacity fix)
• geostyler-geocss-parser -> @geosolutions/geostyler-geocss-parser
• geostyler-openlayers-parser aligned to the 2.x.x versions

geostyler-style has not been updated yet because not needed for this enhancement

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Other... Please describe: libraries update

Issue

What is the current behavior?

#5765
#7617

What is the new behavior?

Use the npm libraries instead of the github repo as dependencies

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• No

Other useful information