We combine the index and tuple hash for point holes in a non-trivial way in
more than one place — let's encapsulate the combination logic in a separate
function for future changes.

Needed for #10159
Needed for #11292

NO_CHANGELOG=<refactoring>
NO_DOC=<refactoring>
NO_TEST=<refactoring>

(cherry picked from commit b6cabab)

It is safe to remove an object from its list, even if the list is empty —
let's always remove point holes from their rings to simplify the code. We
will use this to further separate the point hole storage deletion from the
point hole item deletion.

Needed for #10159
Needed for #11292

NO_CHANGELOG=<refactoring>
NO_DOC=<refactoring>
NO_TEST=<refactoring>

(cherry picked from commit 171412a)

We delete point item separately in more than one place — let's encapsulate
this logic in a separate function for further changes.

Needed for #10159
Needed for #11292

NO_CHANGELOG=<refactoring>
NO_DOC=<refactoring>
NO_TEST=<refactoring>

(cherry picked from commit 674d75e)

Globally unique index identifiers are redundant, since indexes can be
uniquely identified by pointers — let's use the pointer to the index for
this purpose.

Needed for #10159
Needed for #11292

NO_CHANGELOG=<refactoring>
NO_DOC=<refactoring>
NO_TEST=<refactoring>

(cherry picked from commit 19ac49a)

Currently, we assume that point hole equivalence classes are defined by
their keys' binary (MsgPack) representation, and use `memcmp` for
comparison. However, this is not true in the case of numeric key
definitions and collations.

To fix this, let's use the corresponding index's key definition for
comparison. Storing the key length then becomes redundant, so let's drop
it.

Closes #10159
Closes #11292

NO_DOC=<bugfix>

(cherry picked from commit b2fc501)

The `space_id` field has become redundant after we started saving the
`index` to point holes — let's drop it to simplify the code.

Folows-up #10159
Folows-up #11292

NO_CHANGELOG=<refactoring>
NO_DOC=<refactoring>
NO_TEST=<refactoring>

(cherry picked from commit f76d3f9)

Folows-up #10159
Folows-up #11292

NO_CHANGELOG=<optimization>
NO_DOC=<optimization>

(cherry picked from commit 76b114e)