C12.22: Track our allocation sizes.

Add an allocated size element to the TOP_ELEMENT_CONTROL struct and use
it to make sure we're not trying to read past the end of a buffer in
canonify_unencrypted_header. Fixes #17636.

(cherry picked from commit b760c356)

Conflicts:
	epan/dissectors/asn1/c1222/packet-c1222-template.c
	epan/dissectors/packet-c1222.c