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/test/run_tests.c b/test/run_tests.c
index 578c34c..bcb4540 100644
--- a/test/run_tests.c
+++ b/test/run_tests.c
@@ -173,7 +173,7 @@
    TEST_ENTRY(ExponentAndMantissaDecodeFailTests),
 #endif /* QCBOR_DISABLE_TAGS */
    TEST_ENTRY(ExponentAndMantissaEncodeTests),
-#endif /* QCBOR_DISABLE_EXP_AND_MANTISSA */
+#endif /* ! QCBOR_DISABLE_EXP_AND_MANTISSA */
    TEST_ENTRY(SortMapTest),
 #if !defined(USEFULBUF_DISABLE_ALL_FLOAT) && !defined(QCBOR_DISABLE_PREFERRED_FLOAT)
    TEST_ENTRY(CDETest),