C++: IR construction for _Imaginary types

Includes a fairly exhaustive test case for arithmetic operations involving `_Complex` and/or `_Imaginary` types. Thanks to these new tests, I discovered that the extractor treats certain arithmetic operations on `_Imaginary` types as separate expression kinds, so I added support for those kinds in IR construction.

Author: Dave Bartolomeo

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -1100,13 +1100,36 @@ private Opcode binaryBitwiseOpcode(BinaryBitwiseOperation expr) {
 }
 
 private Opcode binaryArithmeticOpcode(BinaryArithmeticOperation expr) {
-  expr instanceof AddExpr and result instanceof Opcode::Add
+  (
+    expr instanceof AddExpr
+    or
+    expr instanceof ImaginaryRealAddExpr
+    or
+    expr instanceof RealImaginaryAddExpr
+  ) and
+  result instanceof Opcode::Add
   or
-  expr instanceof SubExpr and result instanceof Opcode::Sub
+  (
+    expr instanceof SubExpr
+    or
+    expr instanceof ImaginaryRealSubExpr
+    or
+    expr instanceof RealImaginarySubExpr
+  ) and
+  result instanceof Opcode::Sub
   or
-  expr instanceof MulExpr and result instanceof Opcode::Mul
+  (
+    expr instanceof MulExpr
+    or
+    expr instanceof ImaginaryMulExpr
+  ) and
+  result instanceof Opcode::Mul
   or
-  expr instanceof DivExpr and result instanceof Opcode::Div
+  (
+    expr instanceof DivExpr or
+    expr instanceof ImaginaryDivExpr
+  ) and
+  result instanceof Opcode::Div
   or
   expr instanceof RemExpr and result instanceof Opcode::Rem
   or