* Fix SyntaxGenerator.InsertMembers for records

* Address feedback from Cyrus

* Add WorkItem

Right now when we open a generated file, we make a temporary file on
disk to placate parts of the VS API that need a file on disk. (If we had
the ability to have our own URI or moniker that'd be fine, but for now
we don't have such an ability.) The original plan was to pack in the
necessary information we need into the path so we can figure out what
file that represents so we can re-open generated files between runs of
VS without requiring actual state.

In practice, that didn't work yet (if nothing else, because we're
packing in a project ID which is random GUID that isn't persisted across
process runs). But the bigger problem is this also runs into MAX_PATH
issues, if the generator assembly or type names are fairly long. So
for now, let's just generate a GUID for the name and store the extra
information in a little lookup table.

This, and also just renaming the parent directory we put things in,
shaves off a fair number of characters, and also means the name of the
generator assembly or type name are no longer something being added
into the overall path length. The only "controllable" parts of the
path that can vary in length is the file name (which must match the hint
name from the compiler), and the user's username.

Fixes https://github.com/dotnet/roslyn/issues/47782, or at least as well
as we can.

We have logic where we try to hide assemblies that were passed with the
/analyzer flag, that were really dependencies of other analyzers. This
was incorrectly firing on an assembly that only contains source
generators.