Not sure the exact version for these, but lets start with this.

We wanted to remove the use of indexers called from threads and
instead keep the communication between objects on the main
thread (and let indexers do their own off-thread work if they
so decide).

This isn't being used yet, but will allow us in the future to
potentially drop the full paths used in the index files and
instead use basenames for a healthy file size slimming.

We can change these a bit now that we know how they're getting
used in the new version of the code.

This is convenient for the code indexer, so lets require it of
the code entries to save us some pain.

This simplies the process of getting all the children in a directory and
the build flags for each file. It will not return ignored files as those
ignored by the VCS.

This is a convenience function to simplify the number of async callbacks
necessary to work through the data set.

We need to rewrite this to avoid using threads. This just stubs out the
same API for where we will start with.

This removes the "threaded" usage of IdeCodeIndexer and moves to
our new async/finish API.

It also creates a new CXIndex for each file, so we can more
reliably release memory after each parse. It probably means we
have to index some data more, but since this is a background
operation, I'd prefer to keep the memory usage lower at any
given time.

We don't want "threaded plugin API". Instead, we want objects that live in
the main thread, and have async/finish API (for which plugins can choose to
use threads if they like).

There is still plenty more to do, but this is a good check-in point
before fixing up things more.

This isn't needed, so just remove it.

This adds more checks to ensure that plugins aren't using the engine
from threads. This cause some issues in the code-index that need to be
fixed.

Recent language servers added a URI variant for this, deprecating the
rootPath path.

This tries a bit harder to ensure we have valid state going forward.

Ensure we don't have things accessing this from other threads, since it is
not safe to do so.

This is a a better type instance check since we use the actual value from
the hash table.

This allows the user to specify CMAKE=/path/to/cmake in case they need to
use an alternate cmake than the default cmake in $PATH.