fix(http-client-csharp): support int64 enum/union base types

Extend InputEnumTypeValueConverter to handle InputPrimitiveTypeKind.Int64
by reading values via GetInt64() and widening InputEnumTypeIntegerValue's
IntegerValue from int to long. Also include the offending kind, enum,
and value names in the default-arm JsonException message so unsupported
kinds are diagnosable from build output.

Fixes Azure/azure-sdk-for-net#59168.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: haiyuazhang

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/InputEnumTypeIntegerValue.cs

@@ -5,12 +5,12 @@ namespace Microsoft.TypeSpec.Generator.Input
 {
     internal class InputEnumTypeIntegerValue : InputEnumTypeValue
     {
-        public InputEnumTypeIntegerValue(string name, int integerValue, InputPrimitiveType valueType, string? summary, string? doc, InputEnumType? enumType = default)
+        public InputEnumTypeIntegerValue(string name, long integerValue, InputPrimitiveType valueType, string? summary, string? doc, InputEnumType? enumType = default)
             : base(name, integerValue, valueType, summary, doc, enumType)
         {
             IntegerValue = integerValue;
         }
 
-        public int IntegerValue { get; }
+        public long IntegerValue { get; }
     }
 }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/Serialization/InputEnumTypeValueConverter.cs

@@ -60,8 +60,9 @@ internal static InputEnumTypeValue CreateEnumTypeValue(ref Utf8JsonReader reader
             {
                 InputPrimitiveTypeKind.String => new InputEnumTypeStringValue(name, rawValue.Value.GetString() ?? throw new JsonException(), valueType, summary, doc, enumType) { Decorators = decorators ?? [] },
                 InputPrimitiveTypeKind.Int32 => new InputEnumTypeIntegerValue(name, rawValue.Value.GetInt32(), valueType, summary, doc, enumType) { Decorators = decorators ?? [] },
+                InputPrimitiveTypeKind.Int64 => new InputEnumTypeIntegerValue(name, rawValue.Value.GetInt64(), valueType, summary, doc, enumType) { Decorators = decorators ?? [] },
                 InputPrimitiveTypeKind.Float32 => new InputEnumTypeFloatValue(name, rawValue.Value.GetSingle(), valueType, summary, doc, enumType) { Decorators = decorators ?? [] },
-                _ => throw new JsonException()
+                _ => throw new JsonException($"Unsupported enum valueType kind '{valueType.Kind}' for enum '{enumType.Name}' value '{name}'.")
             };
             if (id != null)
             {