Fork Guava's CompactHashMap into Bazel as it is not public in Guava.

CompactHashMap can substantially reduce runtime and especially generated
garbage in various places.

RELNOTES: None.
PiperOrigin-RevId: 247011181

src/main/java/com/google/devtools/build/lib/BUILD

@@ -29,6 +29,7 @@ filegroup(
         "//src/main/java/com/google/devtools/build/lib/bazel/debug:srcs",
         "//src/main/java/com/google/devtools/build/lib/clock:srcs",
         "//src/main/java/com/google/devtools/build/lib/cmdline:srcs",
+        "//src/main/java/com/google/devtools/build/lib/collect/compacthashmap:srcs",
         "//src/main/java/com/google/devtools/build/lib/collect/compacthashset:srcs",
         "//src/main/java/com/google/devtools/build/lib/collect/nestedset:srcs",
         "//src/main/java/com/google/devtools/build/lib/collect:srcs",

src/main/java/com/google/devtools/build/lib/collect/compacthashmap/BUILD

@@ -0,0 +1,19 @@
+package(default_visibility = ["//src:__subpackages__"])
+
+filegroup(
+    name = "srcs",
+    srcs = glob(["**"]),
+    visibility = ["//src/main/java/com/google/devtools/build/lib:__pkg__"],
+)
+
+# Library of collection utilities.
+java_library(
+    name = "compacthashmap",
+    srcs = glob([
+        "*.java",
+    ]),
+    deps = [
+        "//third_party:guava",
+        "//third_party:jsr305",
+    ],
+)