splice update operation now supports varbinary

Related dev. issue(s): https://github.com/tarantool/tarantool/issues/9997
Related doc. issue(s): https://github.com/tarantool/doc/issues/3551 (should be fixed before https://github.com/tarantool/doc/issues/4237)

Product: Tarantool
Since: 3.2.0
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/update/
SME: @ alyapunov

Details

Just in case splice is an update operation that can modify string
field, deleting a part of it and inserting something instead.

tarantool> box.tuple.new{'1234567'}:update{{':', 1, 2, 3, '!'}}
---
- ['1!567']
...

In the this example splice operation ':' takes field 1 of tuple,
takes position 2 in string, removes 3 symbols and inserts '!' to
that position.

Both deletion and insertion can naturally degrade to no-op.

Before this patch a splice operation required both field and
inserting argument to be strings.

This patch allows the field and the argument to be varbinary.

tarantool> varb = require('varbinary')
tarantool> t = box.tuple.new{varb.new('1234567')}
tarantool> t:update{{':', 1, 2, 3, varb.new('!')}}
---
- [!!binary MSE1Njc=]
...

That also allows to insert strings into varbinary fields and
insert varbinary data into string. The actual field type after
update such operation remains the same, so updated string will
be string, while updated varbinary will be varbinary.

Closes #9997
Requested by @ alyapunov in https://github.com/tarantool/tarantool/commit/aaa0ad0c25d5dcf566897d926eb5d1d37c1ed72a.

Start with the root document for box.space.update and review related doc issue #3551 first, as requested in the issue. Document splice support for varbinary, including mixed string and varbinary insertion and preservation of the updated field type, with the examples shown. Done means the update reference covers the behavior introduced in Tarantool 3.2.0.