Fix slice serialization

[arhimondr]

Description

Fix Slice to Json serialization for non UTF-8 values

Non-technical explanation

N/A

Release notes

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# Section
* Fix some things. ({issue}`issuenumber`)

[arhimondr]

I tried to comment out slice serialization in TrinoMainModule and ran a couple of integration tests. It doesn't seem to break anything thus it looks like it was being unused. However it breaks statistics delivery introduced in #14072

[findepi]

Shouldn't this commit also remove the SliceSerialization.* classes?

[arhimondr]

The SliceSerialization is needed by the #14072 that was introduced recently.

It doesn't seem to break anything thus it looks like it was being unused.

By that I meant that it looks like it was not used before #14072

[findepi]

Serializing to a UTF string doesn't work for all possible values

just "a String"

"values" -> "codepoints" ?

[arhimondr]

Technically it is still serialized into a String (that contains only base64 characters). By values I meant all possible values that a Slice can contain

[findepi]

I don't know what "UTF string" is.

let's change commit message to sth like

Interpreting as UTF-8 works only for UTF-8 encoded text (and even then not necessarily for all the codepoints), 
but a Slice can carry arbitrary bytes.

[arhimondr]

Sounds good, let me change the commit message