Inconsistency between table am callback and table function names

The general theme for table function names seem to be
"table_<am_callback_name>". For example table_scan_getnextslot() and its
corresponding callback scan_getnextslot(). Most of the table functions and
callbacks follow mentioned convention except following ones

table_beginscan
table_endscan
table_rescan
table_fetch_row_version
table_get_latest_tid
table_insert
table_insert_speculative
table_complete_speculative
table_delete
table_update
table_lock_tuple

the corresponding callback names for them are

scan_begin
scan_end
scan_rescan
tuple_fetch_row_version
tuple_get_latest_tid
tuple_insert
tuple_insert_speculative
tuple_delete
tuple_update
tuple_lock

It confuses while browsing through the code and hence I would like to
propose we make them consistent. Either fix the callback names or table
functions but all should follow the same convention, makes it easy to
browse around and refer to as well. Personally, I would say fix the table
function names as callback names seem fine. So, for example, make it
table_scan_begin().

Also, some of these table function names read little odd

table_relation_set_new_filenode
table_relation_nontransactional_truncate
table_relation_copy_data
table_relation_copy_for_cluster
table_relation_vacuum
table_relation_estimate_size

Can we drop relation word from callback names and as a result from these
function names as well? Just have callback names as set_new_filenode,
copy_data, estimate_size?

Also, a question about comments. Currently, redundant comments are written
above callback functions as also above table functions. They differ
sometimes a little bit on descriptions but majority content still being the
same. Should we have only one place finalized to have the comments to keep
them in sync and also know which one to refer to?

Plus, file name amapi.h now seems very broad, if possible should be renamed
to indexamapi.h or indexam.h to follow tableam.h. No idea what's our policy
around header file renames.