PS: Lift StringLiterals to the public AST from the raw AST.

Author: MathiasVP

powershell/ql/lib/semmle/code/powershell/ast/internal/Internal.qll

@@ -66,6 +66,7 @@ module Public {
   import ParenExpr
   import Pipeline
   import StringConstantExpression
+  import StringLiteral
   import MemberExpr
   import InvokeMemberExpression
   import ObjectCreation

powershell/ql/lib/semmle/code/powershell/ast/internal/StringLiteral.qll

@@ -0,0 +1,16 @@
+private import AstImport
+
+// TODO: A string literal should ideally be the string constants that are
+// surrounded by quotes (single or double), but we don't yet extract that
+// information. So for now we just use the StringConstExpr class, which is
+// a bit more general than we want.
+class StringLiteral instanceof StringConstExpr {
+  /** Get the string representation of this string literal. */
+  string toString() { result = this.getValue() }
+
+  /** Get the value of this string literal. */
+  string getValue() { result = super.getValueString() }
+
+  /** Get the location of this string literal. */
+  SourceLocation getLocation() { result = super.getLocation() }
+}