[WIP] Allow underscores in varbinary literals

[brunokim]

Description

Allow underscores in addition to whitespace within varbinary literals.

Additional context and related issues

This PR has #24774 as a dependency.

This change was a minor point in the discussion of #23682, but I thought it
would be a good starting point to me as a contributor.

Numeric literals allow underscores for readability, and a developer (like me)
may expect that varbinary literals would use the same pattern. This syntax is more
lenient than the one for numbers, ignoring any number of underscores (or whitespace)
in the string.

Release notes

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## Section
* Allow underscores in varbinary literals ({23682}`23682`)

[mosabua]

Could you also look at #24784 and talk to @martint or maybe @kasiafi

[kasiafi]

@brunokim per SQL specification 5.3 <literal>, underscore is illegal in hex literals. Whitespace is legal and Trino supports it. What is the purpose of having two separator characters?

Also, if we aimed at consistency with numeric literals, we should disallow leading, trailing and consecutive underscores.

[brunokim]

@brunokim per SQL specification 5.3 <literal>, underscore is illegal in hex literals. Whitespace is legal and Trino supports it. What is the purpose of having two separator characters?

Oh, I don't have access to the specification and didn't know this choice comes from there. This change should be closed, then.

Also, if we aimed at consistency with numeric literals, we should disallow leading, trailing and consecutive underscores.

It's a matter of opinion, for sure, but moot since the standard already addresses it. IMO a binary literal is more like a number than like a string, but a binary object is more like a string than like a number, so I can empathize with these choices.