sql: rework sqlSrcListAppend to set diag

Refactored sqlSrcListAppend routine as sql_src_list_append and
reworked it to use diag_set in case of memory allocation error.
This change is necessary because the sql_src_list_append body has
a sqlNameFromToken call that will be changed in subsequent
patches.

This patch refers to a series of preparatory patches that provide
the use of Tarantool errors in the call tree that includes
sqlNormalizeName, since this call can later return errors.

This patch is not self-sufficient, its sqlNameFromToken call
remained to be non-Tarantool (for now). It means, that if
sqlNameFromToken fails in sql_src_list_append there is no
diag message created.

Part of #3931