GN tool: copy_git_directory.py script
GN tool: copy_git_directory.py script

Motivation: to be used by android roller (android_skia_checkout.go)
to keep third_party/libgif updated to where DEPS points
third_party/external/libgif at.

No-Try: true
Bug: skia:9654
Change-Id: I18273dfc7da215b6081ffd454edfa1651791b6df
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254896
Commit-Queue: Hal Canary <fd9641b23487c8ee78406c27513624c460600766@google.com>
Reviewed-by: Leon Scroggins <995cad867ca30d6399abe011583a53547c8afea1@google.com>

HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,HalCanary/skia-hc,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,google/skia