LexFilter: add more info to the indentation error

src/Compiler/FSComp.txt

@@ -998,7 +998,7 @@ lexhlpIdentifierReserved,"The identifier '%s' is reserved for future use by F#"
 1118,optFailedToInlineValue,"Failed to inline the value '%s' marked 'inline', perhaps because a recursive value was marked 'inline'"
 1119,optRecursiveValValue,"Recursive ValValue %s"
 lexfltIncorrentIndentationOfIn,"The indentation of this 'in' token is incorrect with respect to the corresponding 'let'"
-lexfltTokenIsOffsideOfContextStartedEarlier,"Possible incorrect indentation: this token is offside of context started at position %s. Try indenting this token further or using standard formatting conventions."
+lexfltTokenIsOffsideOfContextStartedEarlier,"Unexpected syntax or possible incorrect indentation: this token is offside of context started at position %s. Try indenting this further.\nTo continue using non-conforming indentation, pass the '--strict-indentation-' flag to the compiler, or set the language version to F# 7."
 lexfltSeparatorTokensOfPatternMatchMisaligned,"The '|' tokens separating rules of this pattern match are misaligned by one column. Consider realigning your code or using further indentation."
 1123,nrInvalidModuleExprType,"Invalid module/expression/type"
 1124,nrTypeInstantiationNeededToDisambiguateTypesWithSameName,"Multiple types exist called '%s', taking different numbers of generic parameters. Provide a type instantiation to disambiguate the type resolution, e.g. '%s'."

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/AccessibilityAnnotations/PermittedLocations/PermittedLocations.fs

@@ -125,9 +125,9 @@ module AccessibilityAnnotations_PermittedLocations =
         |> shouldFail
         |> withDiagnostics [
             (Error 531, Line 11, Col 13, Line 11, Col 20, "Accessibility modifiers should come immediately prior to the identifier naming a construct")
-            (Error 58, Line 12, Col 23, Line 12, Col 26, "Possible incorrect indentation: this token is offside of context started at position (11:23). Try indenting this token further or using standard formatting conventions.")
+            (Error 58, Line 12, Col 23, Line 12, Col 26, "Unexpected syntax or possible incorrect indentation: this token is offside of context started at position (11:23). Try indenting this further.\nTo continue using non-conforming indentation, pass the '--strict-indentation-' flag to the compiler, or set the language version to F# 7.")
             (Error 531, Line 12, Col 13, Line 12, Col 19, "Accessibility modifiers should come immediately prior to the identifier naming a construct")
-            (Error 58, Line 13, Col 23, Line 13, Col 26, "Possible incorrect indentation: this token is offside of context started at position (12:23). Try indenting this token further or using standard formatting conventions.")
+            (Error 58, Line 13, Col 23, Line 13, Col 26, "Unexpected syntax or possible incorrect indentation: this token is offside of context started at position (12:23). Try indenting this further.\nTo continue using non-conforming indentation, pass the '--strict-indentation-' flag to the compiler, or set the language version to F# 7.")
             (Error 531, Line 13, Col 13, Line 13, Col 21, "Accessibility modifiers should come immediately prior to the identifier naming a construct")
         ]