Add an internal QueryPartListView class

[lukaseder]

The existing QueryPartList class is a list. Its constructors copy the arguments. In many cases, this is wasteful and unnecessary. A new QueryPartListView class that doesn't copy the argument list would cause less copying overhead, and help make list generation and formatting logic more reusable (see #9985)

[lukaseder]

Now that we have this utility, it will make sense to also add some formatting hints. E.g. to specify from outside:

• The separator character(s) (e.g. Statement doesn't use ,, but nothing)
• Whether the list indents on size() > 1