Avoid alias duplicates in PASTE JOIN and fix aliases requirement

[yariks5s]

Changelog category (leave one):

• Backward Incompatible Change

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Allow queries without aliases for subqueries for PASTE JOIN.

The PASTE keyword is now reserved to improve the parsing of PASTE JOIN operations. This change ensures that the parser correctly identifies PASTE JOIN operations and prevents conflicts with identifiers named paste. If your queries contain paste as an identifier, you should update them to avoid syntax errors.

For example, this query will be no longer executed:

SELECT 1 paste;

You may want to update your queries that contains paste identifier as following:

SELECT 1 AS paste;

or quote the paste identifier:

SELECT 1 `paste`;
SELECT 1 "paste";

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

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[vdimir]

Sorry, I already forgot what table_expression_node corresponds to. Why do we check only one node while checkDuplicateTableNamesOrAlias expects left and right expression to be query ?

[yariks5s]

We check only one node each time because we pass into validateJoinTableExpressionWithoutAlias only one argument (either left or right), so we call this function two times for each of the values.

[vdimir]

Btw, I recently though about it and found out that it can be breaking change and we need to mention it properly in a changelog. Because paste is parsed as a keyword instead of alias name. wee need to consider which queries may stop work if someone uses paste as subquery name: (SELECT ... ) paste ..., (SELECT ... ) AS paste ... and so on, and explain it in a changelog. Maybe even something already changed when we introduced PASTE join, but for me it became clear only after we found this thing with restricted_keywords