Array.findLast and other missing functions

[jmagaram]

Some missing functions from the Array module. In particular the findLast variants.

indexOfFromOpt: add code and docs lastIndexOf : docs, tests lastIndexOfOpt : tests lastIndexOfFrom : docs, tests findLast : code, docs, tests findLastIndex : code, docs, tests findLastIndexOpt : code, docs, tests findLastIndexWithIndex : code, docs, tests findLastIndexWithIndexOpt : code, docs