simplify lookupIdentifier using allCases lookup

Author: QuietMisdreavus

Sources/SymbolKit/SymbolGraph/Symbol/Symbol.swift

@@ -391,28 +391,7 @@ extension SymbolGraph.Symbol {
         /// - Parameter identifier: The identifier string to check.
         /// - Returns: The matching `KindIdentifier` case, or `nil` if there was no match.
         private static func lookupIdentifier(identifier: String) -> KindIdentifier? {
-            switch identifier {
-            case "associatedtype" : return .associatedtype
-            case "class"          : return .class
-            case "deinit"         : return .deinit
-            case "enum"           : return .enum
-            case "enum.case"      : return .case
-            case "func"           : return .func
-            case "func.op"        : return .operator
-            case "init"           : return .`init`
-            case "method"         : return .method
-            case "property"       : return .property
-            case "protocol"       : return .protocol
-            case "struct"         : return .struct
-            case "subscript"      : return .subscript
-            case "type.method"    : return .typeMethod
-            case "type.property"  : return .typeProperty
-            case "type.subscript" : return .typeSubscript
-            case "typealias"      : return .typealias
-            case "var"            : return .var
-            case "module"         : return .module
-            default               : return nil
-            }
+            allCases.first(where: { $0.identifier == identifier })
         }
 
         /// Strips the first component of the given identifier string, so that (for example) `"swift.func"` will return `"func"`.