Support block comments in selector filter syntax (#5023)

The filter_elements selector grammar had no way to comment out part of a
query, so users had to delete and retype text to temporarily toggle a
facet. Add a /* ... */ block comment terminal that is ignored by the
lexer, and tolerate a trailing "+" so that commenting out the final
operand (e.g. "IfcWall + /* IfcSlab */") parses cleanly. Comments may
span multiple lines; a /* sequence inside a quoted string is not treated
as a comment. Only the filter grammar is affected, not get_element or
format which use "/" for regex and division.

Adds a regression test and documents the syntax.

Generated with the assistance of an AI coding tool.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
(cherry picked from commit 5c11946470)

src/ifcopenshell-python/docs/ifcopenshell-python/selector_syntax.rst

@@ -89,6 +89,11 @@ The filters are chained and apply from left to right.
 
     filter[, filter]*
 
+Any part of a query may be commented out using a ``/* ... */`` block comment.
+This lets you temporarily disable part of a query without deleting the text, for
+example ``IfcWall + /* IfcSlab, material=concrete */`` selects only walls while
+keeping the slab criteria on hand. Block comments may span multiple lines.
+
 Below is the table of filters to choose from. Most of these filters will filter
 previously added elements in your filter group based on their criteria.