feat(vcs): support multiple repositories in the Git tool window

The Git tool window followed one globally selected repository even when multiple roots were registered. Aggregate repository logs and branches, preserve repository identity in selections, history tabs, stashes, diffs and patch commands, and capture repository targets for delayed operations and dialogs. Validate tag names against the captured repository.

Fixes #195

src/features/vcs/GitLog.module.css

@@ -500,3 +500,11 @@
   min-height: 0;
   overflow: auto;
 }
+
+.colRepository {
+  flex: 0 0 100px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  color: var(--fg-secondary);
+}