Small cleanup of QCBOR_DISABLE_EXP_AND_MANTISSA, remove QCBOR_DISABLE_UNCOMMON_TAGS

Expand test coverage for decimal fractions. Fix c++ for qcbor_decode_tags.h. Close out some tag-related TODO's that didn't need much. Tidy up  QCBOR_DISABLE_EXP_AND_MANTISSA #ifdefs


* Small cleanup of QCBOR_DISABLE_EXP_AND_MANTISSA

* Remove DISABLE_UNCOMMON_TAGS

* expand decimal frac test coverage; close out todo's

---------

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/src/qcbor_decode.c b/src/qcbor_decode.c
index 2992ce1..73ae425 100644
--- a/src/qcbor_decode.c
+++ b/src/qcbor_decode.c
@@ -5637,7 +5637,7 @@
    return (*pfExp)(uMantissa, nExponent, puResult);
 }
 
-#endif /* QCBOR_DISABLE_EXP_AND_MANTISSA */
+#endif /* ! QCBOR_DISABLE_EXP_AND_MANTISSA */
 
 
 
@@ -6060,7 +6060,7 @@
             return QCBOR_ERR_UNEXPECTED_TYPE;
          }
          break;
-#endif /* QCBOR_DISABLE_EXP_AND_MANTISSA */
+#endif /* ! QCBOR_DISABLE_EXP_AND_MANTISSA */
 
 
       default:
@@ -6459,7 +6459,7 @@
             return QCBOR_ERR_UNEXPECTED_TYPE;
          }
          break;
-#endif /* QCBOR_DISABLE_EXP_AND_MANTISSA */
+#endif /* ! QCBOR_DISABLE_EXP_AND_MANTISSA */
       default:
          return QCBOR_ERR_UNEXPECTED_TYPE;
    }