MIsmatch with spec on rpls_poc_lsb_lt parsing

[forayr]

In ref_pic_list_struct(), rpls_poc_lsb_lt shall be parsed only when ltrp_in_slice_header_flag is equal to false. The VTM do the opposite.

[forayr]

MR: ​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/merge_requests/909

[forayr]

Other issues have been identified:

• When ltrp_in_slice_header_flag = 0, the value of st_ref_pic_flag is needed to parse slice_poc_lsb_lt, but the VTM does not save it in this case.
• numLtrp is not increase when ltrp_in_slice_header_flag = 0, but the information is needed when parsing slice_poc_lsb_lt.
• As two distinct idx (ii and j) are used to save RefPicIdentifier data, long term information (with index j) might overwritten short term information, and is not written where the slice parsing (near slice_poc_lst_lt) call them.

The MR has been updated to fix that.