docs: fix doc comment bugs in List, Promise, and Float

[mikaello]

Fix several documentation bugs found in doc comments:

• List.fromInitializer: description referenced old name makeBy (same as Fix doc to use correct function #255)
• List.reduceReverse2: description said reduce2 returns the final value
• Promise.all6 / allSettled6: parameter list was missing p3 (had p1, p2, p4, p5, p6), and the comment closing was malformed (")*/)
• Float.Constants.maxValue: example showed minValue instead of maxValue
• List (forEachWithIndex): Item 2 is cc → Item 2 is c (copy-paste typo)
• RegExp (sticky + unicode): example called RegExp.unicode instead of RegExp.sticky, and unicode description said flag was y instead of u

[fhammerschmidt]

Thanks! ReScript Core has moved into the main ReScript repo again. So please apply your fixes there first.

It's just called Stdlib internally in order to make migrations easier (no name clashes).