Make plainText publicly accessible (#415)

* Makes plainText public and curates RenderInlineContent.
* Makes sure the enum cases appear first.
* Adds missing copyright statement.

rdar://101910081

Author: micpringle

Sources/SwiftDocC/Model/Rendering/Content/RenderInlineContent.swift

@@ -176,7 +176,7 @@ extension RenderInlineContent {
     /// more sense to use the `rawIndexableTextContent` function that does use `RenderReference`
     /// for a more accurate textual representation of `RenderInlineContent.image` and
     /// `RenderInlineContent.reference`.
-    var plainText: String {
+    public var plainText: String {
         switch self {
         case let .codeVoice(code):
             return code
@@ -213,7 +213,7 @@ extension Sequence where Element == RenderInlineContent {
     /// more sense to use the `rawIndexableTextContent` function that does use `RenderReference`
     /// for a more accurate textual representation of `RenderInlineContent.image` and
     /// `RenderInlineContent.reference`.
-    var plainText: String {
+    public var plainText: String {
         return map { $0.plainText }.joined()
     }
 }

Sources/SwiftDocC/SwiftDocC.docc/SwiftDocC/RenderingModel/RenderInlineContent.md

@@ -0,0 +1,23 @@
+# ``SwiftDocC/RenderInlineContent``
+
+## Topics
+
+### Inline content types
+
+- ``codeVoice(code:)``
+- ``emphasis(inlineContent:)``
+- ``image(identifier:metadata:)``
+- ``inlineHead(inlineContent:)``
+- ``newTerm(inlineContent:)``
+- ``reference(identifier:isActive:overridingTitle:overridingTitleInlineContent:)``
+- ``strikethrough(inlineContent:)``
+- ``strong(inlineContent:)``
+- ``subscript(inlineContent:)``
+- ``superscript(inlineContent:)``
+- ``text(_:)``
+
+### Getting a plain text representation
+
+- ``plainText``
+
+<!-- Copyright (c) 2022 Apple Inc and the Swift Project authors. All Rights Reserved. -->