descs: refactor GetAll* methods

[postamar]

This commit refactors the descs.Collection's GetAll* methods, which
return descriptors and other catalog metadata in bulk, to share a common
access path in which the descriptor's layers are properly aggregated.
This is non-trivial as there are numerous edge cases:

• virtual schemas and objects exist for all databases and their
  descriptors don't reference the parent database at all,
• descriptorless public schemas and temporary schemas only exist as
  namespace entries,
• functions don't have namespace entries,
• and so forth.

These new methods are delegated to by the existing methods which are now
deprecated.

Informs #64089.

Release note: None

[cockroach-teamcity]

This change is 

[ajwerner]

Reviewed 32 of 32 files at r1, 2 of 2 files at r2, 5 of 5 files at r3, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @postamar)

---

pkg/sql/catalog/descs/collection.go line 861 at r3 (raw file):

	ctx context.Context, txn *kv.Txn, stored nstree.Catalog, seedIDs catalog.DescriptorIDSet,
) (ret nstree.MutableCatalog, _ error) {
	descIDs := catalog.MakeDescriptorIDSet(seedIDs.Ordered()...)

nit: it'd be nice to not need to make this slice, but it's a nit

---

pkg/sql/catalog/tabledesc/table_desc.go line 78 at r3 (raw file):

// SkipNamespace implements the descriptor interface.
func (desc *wrapper) SkipNamespace() bool {
	return desc.IsVirtualTable()

This could use some commentary

[postamar]

Thanks for the review. I've addressed your comments. Notice also that the rttanalysis benchmark regresses with this PR; I'm well aware & this will be addressed shortly. There's some duplication of work due to some uncalled-for use of the catkv.Direct interface in pg_catalog.go, it's quite straightforward.

[postamar]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)