Remove always-on language feature flag: AndBang

[T-Gro]

LanguageFeature.AndBang has shipped since F# 5.0 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 AndBang case in LanguageFeatures.fs and LanguageFeatures.fsi
• Its entry in the features map and its GetFeatureString arm
• The featureAndBang string in FSComp.txt
• Every SupportsFeature LanguageFeature.AndBang / checkLanguageFeatureAndRecover … AndBang guard — keep only the enabled path and delete the legacy branch
• Adjust affected tests and baselines accordingly

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

Version mapping

fsharp/src/Compiler/Facilities/LanguageFeatures.fs

Line 163 in ea778bb

LanguageFeature.AndBang, languageVersion50

Feature string

fsharp/src/Compiler/FSComp.txt

Line 1577 in ea778bb

featureAndBang,"applicative computation expressions"

Part of #20139