Improve KDoc-snippets usages

(relevant after #1683)
* Use `SelectingRows.RowFilterSnippet` and `SelectingRows.RowValueFilterSnippet` instead of `EntireRowCondition`/`RowValueCondition` + add KoDEx example template.
* Move `AddExpressionDocs` (rename to `Snippet`!) and add it to other methods Kdocs with `AddExpression`.
* Add similar snippets in all `ExpressionGiven...` helpers.

Start by reading issue #1683 and the existing KDoc snippets around SelectingRows, AddExpressionDocs, and the ExpressionGiven... helpers. Identify every named helper and its current documentation pattern. Done means the requested RowFilterSnippet and RowValueFilterSnippet, renamed Snippet documentation, KoDEx example template, and corresponding snippets are applied consistently.

Written by the indexing model from the issue text.