canonicalErrorCode
Maps this core parse/relative failure to its canonical conformance error code.
This is the single place the Kotlin KPointerException subtypes are translated into the language-neutral vocabulary that the shared conformance fixtures assert against. RelativeMalformedSyntax intentionally collapses every syntactic relative-pointer failure into one code (KP-2001).
Return
The canonical errorCode string (e.g. "KP-1001") for this exception.
Receiver
The core exception raised while parsing a pointer string or applying a relative pointer.