amend! path-walk: improve path-walk speed with many tags (#5205)

path-walk: improve path-walk speed with many tags (#5205)

In the presence of many tags, the use of oid_array_lookup() can become
extremely slow. We should rely upon the SEEN bit instead.

This affects the tag-peeling walk as well as the switch statement for
adding the peeled object to the correct oid_array.

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Derrick Stolee <stolee@gmail.com> found this while testing the
2.47.0.vfs.0.0 pre-release against a repo with many annotated tags.

This is a backport of microsoft#695.

Signed-off-by: Derrick Stolee <stolee@gmail.com>