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>

src/ifcopenshell-python/ifcopenshell/util/selector.py

@@ -40,7 +40,7 @@ import ifcopenshell.util.system
 import ifcopenshell.util.unit
 
 filter_elements_grammar = lark.Lark("""start: filter_group
-    filter_group: facet_list ("+" facet_list)*
+    filter_group: facet_list ("+" facet_list)* "+"?
     facet_list: facet ("," facet)*
 
     facet: instance | entity | attribute | type | material | query | classification | location | property | group | parent
@@ -108,8 +108,10 @@ filter_elements_grammar = lark.Lark("""start: filter_group
     CR : /\\r/
     LF : /\\n/
     NEWLINE: (CR? LF)+
+    COMMENT: "/*" /.*?/s "*/"
 
     %ignore WS // Disregard spaces in text
+    %ignore COMMENT // Allow /* ... */ block comments to toggle parts of a query
 """)
 
 get_element_grammar = lark.Lark("""start: keys