Remove always-on language feature flag: WildCardInForLoop

[T-Gro]

LanguageFeature.WildCardInForLoop has shipped since F# 4.7 and is enabled for every selectable language version (the minimum accepted --langversion is 8.0). Its feature flag can therefore never be turned off, so it is dead configuration. This issue removes the flag and collapses the guarded code to its enabled behaviour.

What to remove

• The WildCardInForLoop case in LanguageFeatures.fs and LanguageFeatures.fsi
• Its entry in the features map and its GetFeatureString arm
• The featureWildCardInForLoop string in FSComp.txt
• Every SupportsFeature LanguageFeature.WildCardInForLoop / checkLanguageFeatureAndRecover … WildCardInForLoop guard — keep only the enabled path and delete the legacy branch
• Adjust affected tests and baselines accordingly

Consequence: --disableLanguageFeature:WildCardInForLoop is no longer a recognised feature name.

Version mapping

fsharp/src/Compiler/Facilities/LanguageFeatures.fs

Line 156 in ea778bb

LanguageFeature.WildCardInForLoop, languageVersion47

Feature string

fsharp/src/Compiler/FSComp.txt

Line 1568 in ea778bb

featureWildCardInForLoop,"wild card in for loop"

Part of #20139