[bazel] Rename //tools/window:window to //tools/window:legacy_window.

End goal: Make //tools/viewer modular.

Bug: b/40045064
Change-Id: I4a117d17807ede9f0df1380976ac9452d96a283f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/834318
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed