feat: QueryBuilder raw SQL string support

[kenjis]

Related: #4355, #3970, #5810

Description
See https://forum.codeigniter.com/showthread.php?tid=80720

• add RawSql class
• select() supports RawSql
• where() supports RawSql
• like() supports RawSql

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[iRedds]

Is it possible to add a second argument to the constructor to pass the binding?
As for BaseConnection::query();

new RawSql('a = ? AND b = ?', [1, 2]);
new RawSql('a = :a AND b = :b', ['a'=>1, 'b' => 2]);

[kenjis]

@iRedds I'm not sure.

Can you tell me what's good if it is possible?
Use case?

[iRedds]

Usage example above.
It seems to me that it will be convenient with a large SQL statement and a large number of variables.

For example, for such a query (from #5810 )

$builder->orLike("(SELECT COALESCE(GROUP_CONCAT(CONCAT(corr.description, ' ', corr.note) ORDER BY corr.order_field ASC SEPARATOR ' '), '') FROM correspondence corr WHERE corr.contact_fk = c. contact_id AND 1 = 1)", "", "both", false);

Although this query does not use value substitution, this is a possible situation.

[kenjis]

@iRedds What's about escaping?
If we need to escape the values, RawSql must have DB Connection.

[iRedds]

It seems to me that there are two options without using DBC

1. The developer himself will escape the values.
2. The binds will be transferred to the $binds property when processing the RawSql instance.

[kenjis]

I do not see much need for binding, so I will not include it in this PR.

[lonnieezell]

I think this solution is fine, and I don't see an issue with leaving binds out. Being raw SQL I don't think that's unexpected. Thanks @kenjis

But it does need docs added.

[kenjis]

I added docs.

[michalsn]

I thought that the $escape parameter would do the trick for this type of scenario but I guess I was wrong. I think it is a good addition.

[kenjis]

@michalsn Thank you!