Storage: Adapt to ingesting snapshot with irregular region range
If the key format is "t${tableID}_r${handleID1}{AnySuffix}", and `AnySuffix` is not empty, `"t${tableID}_r${handleID1}{AnySuffix}" > "t${tableID}_r${handleID1}"` according to the the comparison semantics of "Key" on TiDB/TiKV.

For example,
If a table is non-clustered, that is with Int64 as the HandleID type.
And the range of a Region is `["xxx_r{handleId1}{AnySuffix}", "xxx_r{handleId2}{AnySuffix}")`, where handleId1 = 100, handleId2 = 200.

If `AnySuffix` is empty, then Region contains the left-closed-right-open range of `[handleID1, handleID2)`
If `AnySuffix` is not empty, then Region contains the range `(handleID1, handleID2]`, which is actually the left-closed-right-open range of `[handleID1+1, handleID2+1)`.

create table if not exists t (a bigint primary key, b int);
insert into t values (1,2),(2,3),(3,4),(4,5),(20, 50), (21, 51),(200002,2),(200003,3),(200004,4), (9223372036854775807, 101),(9223372036854775806, 100),(-9223372036854775808, -101),(-9223372036854775807, -100);

// The keys is related to the table_id. For these verification cases, the table_id=471

tiup ctl pd -u {pd_ip}:{pd_port} -i
# split with table_id=471, row_id=20, suffix='\x00'
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F728000000000FF0000140000000000FB
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=20, suffix='\x01'
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F728000000000FF0000140100000000FB
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=20, suffix='\x0130FF'
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F728000000000FF0000140130FF0000FD
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=-9223372036854775808, suffix=''
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F720000000000FF0000000000000000FA
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=-9223372036854775808, suffix='\x01'
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F720000000000FF0000000100000000FB
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=9223372036854775807, suffix=''
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F72FFFFFFFFFFFFFFFFFF0000000000FA
# then add tiflash replica
alter table set tiflash replica 1;

# split with table_id=471, row_id=9223372036854775807, suffix='\x01'
operator add split-region 2077 --policy usekey --keys 7480000000000001FFD75F72FFFFFFFFFFFFFFFFFF0100000000FB
# then add tiflash replica
alter table set tiflash replica 1;

Fix the issue that TiFlash might panic when handling snapshot with irregular region range