[Testing] Fix phpunit test dir paths
Further tweaks to the PHPUnit configuration description
Fixes after review
Documented missing FormType variables
Documented checked variable
Documented choice variables
Documented selectedchoice test
Added performance tip
Documented CollectionType variables
Documented Date(Time)Type variables
Extracted duplicated var tables
Documented date_pattern variable of DateType
Documented FileType variables
Documented MoneyType variables
Documented SubmitType variables
Documented TimeType variables
Added globals section
Added a note on caching
Documented custom engines and DelegatingEngine
Applied comments by @xabbuh