[refactoring] Extract read leb to a separate file, share the code between loader and mini loader (#3701)

There's probably a number of other places where the bh_leb_read could be used (e.g. aot loader)
but I'm making the change as small as possible. Further refactoring can be done later.

product-mini/platforms/alios-things/aos.mk

@@ -102,6 +102,7 @@ $(NAME)_SOURCES := ${SHARED_ROOT}/platform/alios/alios_platform.c \
                    ${SHARED_ROOT}/utils/bh_common.c \
                    ${SHARED_ROOT}/utils/bh_hashmap.c \
                    ${SHARED_ROOT}/utils/bh_list.c \
+                   ${SHARED_ROOT}/utils/bh_leb128.c \
                    ${SHARED_ROOT}/utils/bh_log.c \
                    ${SHARED_ROOT}/utils/bh_queue.c \
                    ${SHARED_ROOT}/utils/bh_vector.c \

product-mini/platforms/nuttx/wamr.mk

@@ -441,6 +441,7 @@ CSRCS += nuttx_platform.c \
          bh_common.c \
          bh_hashmap.c \
          bh_list.c \
+         bh_leb128.c \
          bh_log.c \
          bh_queue.c \
          bh_vector.c \