ENH: add Switch::negate() method (no-op for invalid state)

- flips state while preserving the textual representation.
  Eg, OFF <-> ON, YES <-> NO etc.

- fix test case to avoid triggering abort(), which we cannot try/catch

src/OpenFOAM/primitives/bools/Switch/Switch.C

@@ -309,6 +309,16 @@ Foam::Switch::switchType Foam::Switch::type() const noexcept
 }
 
 
+void Foam::Switch::negate() noexcept
+{
+    if (value_ < switchType::INVALID)
+    {
+        // Toggle final bit. So NO <-> YES, OFF <-> ON ...
+        value_ ^= 0x1;
+    }
+}
+
+
 const char* Foam::Switch::c_str() const noexcept
 {
     return names[(value_ & 0x0F)];

src/OpenFOAM/primitives/bools/Switch/Switch.H

@@ -91,7 +91,7 @@ public:
             NO      = 2 /*!< "no" */,    YES  = 3 /*!< "yes" */,
             OFF     = 4 /*!< "off" */,   ON   = 5 /*!< "on" */,
             NONE    = 6 /*!< "none" */,  ANY  = 7 /*!< "any" */,
-            INVALID = 8 /*!< "invalid" */,
+            INVALID = 8 /*!< "invalid" (output only) */,
         };
 
 
@@ -227,6 +227,10 @@ public:
         //- The underlying enumeration value
         switchType type() const noexcept;
 
+        //- Flip the type, so OFF becomes ON, etc.
+        //  Ignored if the Switch is INVALID
+        void negate() noexcept;
+
         //- A C-string representation of the Switch value
         const char* c_str() const noexcept;