Add mbuf_append_and_free() and mbuf_move()

CL: Add mbuf_append_and_free() and mbuf_move()

PUBLISHED_FROM=bdf73906dd93b2ebeace160596508e15480b54b4

docs/c-api/mbuf.h/intro.md

@@ -4,10 +4,12 @@ symbol_kind: "intro"
 decl_name: "mbuf.h"
 items:
   - { name: mbuf_append.md }
+  - { name: mbuf_append_and_free.md }
   - { name: mbuf_clear.md }
   - { name: mbuf_free.md }
   - { name: mbuf_init.md }
   - { name: mbuf_insert.md }
+  - { name: mbuf_move.md }
   - { name: mbuf_remove.md }
   - { name: mbuf_resize.md }
   - { name: mbuf_trim.md }