[TRTLLM-5252][fix] Propagate mapping to intermediate layers (NVIDIA#6611) (NVIDIA#6765)

This commit propagates the mapping to intermediate layers to enable
tensor parallelism (amongst other things) in them.

It also fixes issues with a unit test for TP for pixtral, and adds it to a
test list.

Signed-off-by: William Zhang <[email protected]>

Author: 2ez4bz