sdbus++: support special double values

Enable properties to have default values of special IEEE floating
points: 'NaN', 'infinity' and 'epsilon'.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I7c2daa3c36cde69c2ee06afd75a8d2e77992c6e7
diff --git a/test/server/Test.interface.yaml b/test/server/Test.interface.yaml
index 30df1f9..ed98eb3 100644
--- a/test/server/Test.interface.yaml
+++ b/test/server/Test.interface.yaml
@@ -22,3 +22,15 @@
       type: uint64
     - name: ObjectPath
       type: object_path
+    - name: DoubleAsNAN
+      type: double
+      default: NaN
+    - name: DoubleAsInf
+      type: double
+      default: Infinity
+    - name: DoubleAsNegInf
+      type: double
+      default: -Infinity
+    - name: DoubleAsEpsilon
+      type: double
+      default: Epsilon