Re-add Syntax.withoutTrivia()

Even though I'm not sure how this can be used considering it's
`internal` and SwiftSyntax still compiles without it, but CI is clearly
failing when it's not there.

```
Undefined symbols for architecture x86_64:
  "(extension in SwiftSyntax):SwiftSyntax.SyntaxProtocol.withoutTrivia() -> A", referenced from:
      swiftASTGen.evaluateMacro(sourceFilePtr: Swift.UnsafePointer<Swift.UInt8>, sourceLocationPtr: Swift.UnsafePointer<Swift.UInt8>?, expandedSourcePointer: Swift.UnsafeMutablePointer<Swift.UnsafePointer<Swift.UInt8>?>, expandedSourceLength: Swift.UnsafeMutablePointer<Swift.Int>) -> Swift.Int in Macros.swift.o
ld: symbol(s) not found for architecture x86_64
```

Author: jpsim

Sources/SwiftSyntax/Syntax.swift

@@ -472,6 +472,11 @@ public extension SyntaxProtocol {
     return withTrailingTrivia([])
   }
 
+  /// Returns a new syntax node with all trivia removed.
+  func withoutTrivia() -> Self {
+    return withoutLeadingTrivia().withoutTrailingTrivia()
+  }
+
   /// The length of this node including all of its trivia.
   var totalLength: SourceLength {
     return raw.totalLength