Link to JGit source as git submodule

Using a submodule to bring in the source files vastly simplifies
updating JGit. Gitiles developers can bump the SHA-1 of the submodule
and not deal with the Maven rebuild process for JGit.

This follows the approach taken in Gerrit in I16370e57f27.

Change-Id: Ib35f7bad8b8f61e73f416937a387e3675bf1e3a2

lib/BUILD

diff --git a/lib/BUILD b/lib/BUILD
index 282643d..0f9620e 100644
--- a/lib/BUILD
+++ b/lib/BUILD
@@ -42,3 +42,45 @@
         "@slf4j-simple//jar",
     ],
 )
+
+java_library(
+    name = "jgit",
+    visibility = ["//visibility:public"],
+    exports = ["@jgit//org.eclipse.jgit:jgit"],
+    runtime_deps = [
+        ":slf4j-api",
+        "@javaewah//jar",
+    ],
+)
+
+java_library(
+    name = "jgit-archive",
+    visibility = ["//visibility:public"],
+    exports = ["@jgit//org.eclipse.jgit.archive:jgit-archive"],
+    runtime_deps = [":jgit"],
+)
+
+java_library(
+    name = "jgit-junit",
+    testonly = True,
+    visibility = ["//visibility:public"],
+    exports = ["@jgit//org.eclipse.jgit.junit:junit"],
+    runtime_deps = [":jgit"],
+)
+
+java_library(
+    name = "jgit-servlet",
+    visibility = ["//visibility:public"],
+    exports = ["@jgit//org.eclipse.jgit.http.server:jgit-servlet"],
+    runtime_deps = [":jgit"],
+)
+
+java_library(
+    name = "tukaani-xz",
+    exports = ["@tukaani-xz//jar"],
+)
+
+java_library(
+    name = "commons-compress",
+    exports = ["@commons-compress//jar"],
+)

lib/jgit/BUILD

diff --git a/lib/jgit/BUILD b/lib/jgit/BUILD
deleted file mode 100644
index d813fd7..0000000
--- a/lib/jgit/BUILD
+++ /dev/null
@@ -1,44 +0,0 @@
-load("@rules_java//java:defs.bzl", "java_library")
-
-package(
-    default_visibility = ["//visibility:public"],
-)
-
-java_library(
-    name = "jgit-servlet",
-    exports = ["@jgit-servlet//jar"],
-)
-
-java_library(
-    name = "jgit",
-    exports = ["@jgit-lib//jar"],
-)
-
-java_library(
-    name = "jgit-archive",
-    exports = [
-        ":commons-compress",
-        ":jgit-archive_library",
-        ":tukaani-xz",
-    ],
-)
-
-java_library(
-    name = "tukaani-xz",
-    exports = ["@tukaani-xz//jar"],
-)
-
-java_library(
-    name = "commons-compress",
-    exports = ["@commons-compress//jar"],
-)
-
-java_library(
-    name = "jgit-archive_library",
-    exports = ["@jgit-archive//jar"],
-)
-
-java_library(
-    name = "junit",
-    exports = ["@jgit-junit//jar"],
-)