sql: internalLookupCtx should be constructed using a collection

[postamar]

This requires a fairly simple rewrite of the newInternalLookupCtx definition and all its call sites except one:

cockroach/pkg/sql/show_create.go

Lines 232 to 234 in 8b356c4

	lCtx, lErr := newInternalLookupCtxFromDescriptorProtos(
	ctx, allDescs, nil, /* want all tables */
	)

In this case, we don't rely on descriptors provided by descs.Collection, instead these come from a backup manifest. To deal with this, try inserting these descriptors as synthetic descriptors into the descs.Collection. That way, newInternalLookupCtx can become oblivious to where the descriptors are actually sourced from.

Jira issue: CRDB-17352

[postamar]

Relates to #64673
cc @ajwerner @chengxiong-ruan

[ajwerner]

This is an approach. I've been thinking instead that we get rid of the internalLookupCtx altogether.

[postamar]

Baby steps! Jason is looking for a way to get started in this direction.