Add InlayHintLabel structures

Sources/LanguageServerProtocol/SupportTypes/InlayHint.swift

@@ -66,3 +66,58 @@ public struct InlayHintKind: RawRepresentable, Codable, Hashable {
   /// Swift, since Swift already has explicit parameter labels.
   public static let parameter: InlayHintKind = InlayHintKind(rawValue: 2)
 }
+
+/// A hint's label, either being a single string or a composition of parts.
+public enum InlayHintLabel: Codable, Hashable {
+  case parts([InlayHintLabelPart])
+  case string(String)
+
+  public init(from decoder: Decoder) throws {
+    if let parts = try? [InlayHintLabelPart](from: decoder) {
+      self = .parts(parts)
+    } else if let string = try? String(from: decoder) {
+      self = .string(string)
+    } else {
+      let context = DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Expected [InlayHintLabelPart] or String")
+      throw DecodingError.dataCorrupted(context)
+    }
+  }
+
+  public func encode(to encoder: Encoder) throws {
+    switch self {
+    case let .parts(parts):
+      try parts.encode(to: encoder)
+    case let .string(string):
+      try string.encode(to: encoder)
+    }
+  }
+}
+
+/// A part of an interactive or composite inlay hint label.
+public struct InlayHintLabelPart: Codable, Hashable {
+  /// The value of this label part.
+  public let value: String
+
+  /// The tooltip to show when the part is hovered.
+  public let tooltip: MarkupContent?
+
+  /// An optional source code location representing this part.
+  /// Used by the editor for hover and code navigation, e.g.
+  /// by making the part a clickable link to the given position.
+  public let location: Location?
+
+  /// An optional command for this label part.
+  public let command: Command?
+
+  public init(
+    value: String,
+    tooltip: MarkupContent? = nil,
+    location: Location? = nil,
+    command: Command? = nil
+  ) {
+    self.value = value
+    self.tooltip = tooltip
+    self.location = location
+    self.command = command
+  }
+}