@TarantoolBot document
Title: splice update operation now supports varbinary

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 tarantool#9997

This patch tests update splice operation more thoroughly:
* All variants of splice: delete/insert/replace/noop.
* All variants of position: negative/positive/zero/OOB.
* One operation and several sequential operations.
* Tuple update, space update, space upsert.
* String of varbinary field/arg.

Follow up tarantool#9997
Closes tarantool#10032

NO_DOC=tests
NO_CHANGELOG=tests