name-hash: use trace2 regions for init

name-hash: use trace2 regions for init

The lazy_init_name_hash() populates a hashset with all filenames and
another with all directories represented in the index. This is run only
if we need to use the hashsets to check for existence or case-folding
renames.

Place trace2 regions where there is already a performance trace.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>