MdeModulePkg/DebugLib: Print partial when format string is too long

MdeModulePkg/DebugLib: Print partial when format string is too long

Today's implementation prints nothing when the format string cannot
fit in the report status extended data buffer.
It confuses user.
The patch changes to print partial message by truncating the format
string when it's too long.

The missing enhancement is the extended data buffer only reserves 96
bytes for the var-args. When the format string is not very long but
contains 13 %lx or %p, the var-args buffer is too small. Today's
implementation prints nothing for this case.
This patch doesn't change such behavior.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>