Rule 1.2: Add change note

Author: lcartey

change_notes/2024-09-19-c-extensions.md

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+ - `RULE-1-2` - `LanguageExtensionsShouldNotBeUsed.ql`:
+   - Improve reporting by describing which language extensions are used.
+   - Improve reporting by aggregating results generated from a macro expansion at the generating macro location.
+   - Reduce false positives for the variable length array check by permitting those extensions which are included in the C99 standard.