[PropertyAccess] Add opt-in wildcard reads

Enable them with PropertyAccessorBuilder::enableWildcardReads() or the
framework.property_access.wildcard_reads option. A "[*]" element then reads
every element of the collection at that position and applies the rest of the
path to each of them, returning one entry per element. "[\*]" reads the
literal "*" index, and writing through a path holding a wildcard throws.