/$filter(...) segments in paths and expressions

Add /$filter(...) segment that can be used in commonExpr after a collection-valued property Change syntax of /$filter path segment to also use parentheses instead of an = sign This introduces Nav/$filter(...)/$count as an alternative to Nav/$count($filter=...) Support expression or parameter within parens.  

https://github.com/oasis-tcs/odata-abnf/pull/6 https://www.oasis-open.org/committees/download.php/64118/odata-v4.01-wd06-part2-url-conventions-2018-10-19.docx https://www.oasis-open.org/committees/download.php/64119/odata-v4.01-wd06-part1-protocol-2018-10-19.docx