Allow alternate backend Solr implementations - WIP

[whikloj]

JIRA Ticket: NONE

This was an alternative solution started based on discussions in the below (now merged) PR.
#342

This is a Work-In-Progress, it should work with the existing ApacheSolrClient but would need a new implementation to really see if it was viable. If there is interest, this can be resurrected. Otherwise I am happy to leave this a sign-post for some intrepid soul.

What does this Pull Request do?

First of all, this is NOT ready. I was trying to see if I could get it to work with the existing stuff. The admin page is probably broken and I haven't tested all the various other Solr things (facet pages, metadata, etc) that might get broken by the new level of abstraction.

But this is my attempt to abstract the ApacheSolrClient layer out. There is much garbage in here, but there is too much member variable use in the code to clean it without a huge time investment (ie. $solr_build->solrParams).

This moves the current ApacheSolrClient work down a level and makes the existing IslandoraSolrQueryProcessor just a proxy to load the actual code. Same for IslandoraSolrResults and IslandoraSolrFacets.

If this seems viable, and there is interest (in the form of work, review and testing) I can continue to push forward with cleaning up the admin pages and trying a Solarium implementation along side.

If not, this can die here and I press on to Claw.

What's new?

Code is the same just shifted so it could be replaced.

How should this be tested?

Anything you used to use Solr for should work the same, but probably won't. That is what I need to know.

Additional Notes:

Example:

• Does this change require documentation to be updated? yes
• Does this change add any new dependencies? yes
• Does this change require any other modifications to be made to the repository (ie. Regeneration activity, etc.)? no
• Could this change impact execution of existing code? 🤷‍♂️

Interested parties

@Islandora/7-x-1-x-committers

[DonRichards]

@whikloj are you able to resolve these conflicts?

[whikloj]

@DonRichards this is rebased, but as it says in the description this is a Work In Progress. I certainly am happy if you test it out, but please do not merge this.

There will have to be more discussion around what a change like this will look like and if I can get an alternate client (Solarium) that still works.