Add isSigned to IntegerParsers

Author: owen-mc

go/ql/lib/semmle/go/frameworks/Stdlib.qll

@@ -117,6 +117,9 @@ module IntegerParser {
      * input is 0 then it means the bit size of `int` and `uint`.
      */
     FunctionInput getTargetBitSizeInput() { none() }
+
+    /** Gets whether the function is for parsing signed or unsigned integers. */
+    boolean isSigned() { none() }
   }
 }
 

go/ql/lib/semmle/go/frameworks/stdlib/Strconv.qll

@@ -11,20 +11,26 @@ module Strconv {
     Atoi() { this.hasQualifiedName("strconv", "Atoi") }
 
     override int getTargetBitSize() { result = 0 }
+
+    override boolean isSigned() { result = true }
   }
 
   /** The `ParseInt` function. */
   class ParseInt extends IntegerParser::Range {
     ParseInt() { this.hasQualifiedName("strconv", "ParseInt") }
 
     override FunctionInput getTargetBitSizeInput() { result.isParameter(2) }
+
+    override boolean isSigned() { result = true }
   }
 
   /** The `ParseUint` function. */
   class ParseUint extends IntegerParser::Range {
     ParseUint() { this.hasQualifiedName("strconv", "ParseUint") }
 
     override FunctionInput getTargetBitSizeInput() { result.isParameter(2) }
+
+    override boolean isSigned() { result = false }
   }
 
   /**