unified: Add qltest with string interpolation

Author: asgerf

unified/ql/test/library-tests/BasicTest/strings.swift

@@ -1 +1,4 @@
-let x = "hello"
+let x1 = "hello"
+let x2 = "hello \(123) world"
+let x3 = "hello \(arg: 123) world"
+let x4 = "hello \(1, 2, 3) world"

unified/ql/test/library-tests/BasicTest/test.expected

@@ -1,7 +1,11 @@
 identifier
 | name_expr.swift:1:5:1:5 | x | x |
 | name_expr.swift:1:9:1:9 | y | y |
-| strings.swift:1:5:1:5 | x | x |
+| strings.swift:1:5:1:6 | x1 | x1 |
+| strings.swift:2:5:2:6 | x2 | x2 |
+| strings.swift:3:5:3:6 | x3 | x3 |
+| strings.swift:3:19:3:21 | arg | arg |
+| strings.swift:4:5:4:6 | x4 | x4 |
 | test.swift:1:8:1:17 | Foundation | Foundation |
 | test.swift:1:8:1:17 | Foundation | Foundation |
 | test.swift:4:8:4:16 | Container | Container |
@@ -151,5 +155,13 @@ identifier
 namedPattern
 | test.swift:1:1:1:17 | NamedPattern | Foundation |
 unsupported
-stringValue
-| strings.swift:1:9:1:15 | "hello" | "hello" |
+rawStringValue
+| strings.swift:1:10:1:16 | "hello" | "hello" |
+| strings.swift:2:11:2:16 | hello  | hello  |
+| strings.swift:2:23:2:28 |  world |  world |
+| strings.swift:3:11:3:16 | hello  | hello  |
+| strings.swift:3:28:3:33 |  world |  world |
+| strings.swift:4:11:4:16 | hello  | hello  |
+| strings.swift:4:27:4:32 |  world |  world |
+exprStringValue
+| strings.swift:1:10:1:16 | "hello" | hello |

unified/ql/test/library-tests/BasicTest/test.ql

@@ -6,4 +6,6 @@ query predicate namedPattern(NamedPattern node, string value) { value = node.get
 
 query predicate unsupported(UnsupportedNode node, string value) { value = node.getValue() }
 
-query predicate stringValue(StringLiteral e, string value) { value = e.getValue() }
+query predicate rawStringValue(StringLiteral e, string value) { value = e.getValue() }
+
+query predicate exprStringValue(Expr e, string value) { value = e.getStringValue() }