copies: make calculating lazy for dir move detection's "addedfiles"...
copies: make calculating lazy for dir move detection's "addedfiles"
The information calculated here was only needed if (a) --debug was specified, or
(b) a directory move was plausibly detected. With tree manifests (especially in
my pathological repo and with our custom setup), pre-calculating the `u1` and
`u2` can be quite slow, and it's not even necessary in many cases. Let's delay
calculating it until we know it's actually necessary. This should have no
observable differences in output.
### Performance
I ran a rebase command in my pathological repo, rebasing two nodes across
several public phase commits, but where no directory copies exist in any of the
paths I'm tracking.
#### Before
```
Time (mean ± σ): 3.711 s ± 0.061 s [User: 0.3 ms, System: 1.5 ms]
Range (min … max): 3.640 s … 3.827 s 10 runs
```
#### After
```
Time (mean ± σ): 868.3 ms ± 10.1 ms [User: 0.5 ms, System: 1.2 ms]
Range (min … max): 856.6 ms … 883.6 ms 10 runs
```
Differential Revision:
https://phab.mercurial-scm.org/D9567
