SOLR-17066 introduced a withDefaultCollection builder method that can be
used in lieu of providing a core URL as a "base". (Core URLs are not
ideal as they prevent clients from making core-agnostic requests.)
However, Solr's own client usage still needs modified to use this new
builder method.

This commit migrates all ConcurrentUpdateSolrClient usage away from core
URLs and towards using `withDefaultCollection` instead.

SOLR-17066 introduced a withDefaultCollection builder method that can be
used in lieu of providing a core URL as a "base". (Core URLs are not
ideal as they prevent clients from making core-agnostic requests.)
However, Solr's own client usage still needs modified to use this new
builder method.

This commit migrates all LBHttpSolrClient usage away from core
URLs and towards using `withDefaultCollection` instead.

SOLR-17066 introduced a withDefaultCollection builder method that can be
used in lieu of providing a core URL as a "base". (Core URLs are not
ideal as they prevent clients from making core-agnostic requests.)
However, Solr's own client usage still needs modified to use this new
builder method.

This commit migrates all ConcurrentUpdateHttp2SolrClient usage away from core
URLs and towards using `withDefaultCollection` instead.

SOLR-17066 introduced a withDefaultCollection builder method that can be
used in lieu of providing a core URL as a "base". (Core URLs are not
ideal as they prevent clients from making core-agnostic requests.)
However, Solr's own client usage still needs modified to use this new
builder method.

This commit migrates all LBHttp2SolrClient usage away from core
URLs and towards using `withDefaultCollection` instead.

Has a test failure in TestLBHttp2SolrClient that still needs resolved.

Zombie-resurrection was broken in LBHttp2SolrClient because the default
collection wasn't being taken into account on these requests.  The root
of the problem is the way that LBHttp2 takes in an already-constructed
SolrClient, making it difficult to set the default collection.  (In
contrast, LBHttpSolrClient creates a different client for each base URL
using a common Builder - this allows it to property set the default
collection.)

This commit fixes this by created a 'DelegatingSolrClient' that LBHttp2
can use internally around its single Http2SolrClient.  The default
collection is set on this 'Delegating' wrapper, so that it gets picked
up by the zombie-resurrection logic.

This reverts commit ceb81c9.

This reverts commit e70b2e2.

This reverts commit 410676b.

This reverts commit 06a2065.

This reverts commit 5905b71.