Bazel: add skeleton bazel workspace

This moves in codeql some internal bazel definitions in preparation for
future work.

Author: redsun82

WORKSPACE.bazel

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+Please notice that any bazel targets and definitions in this repository are currently experimental and for internal use
+only.

bazel/README.md

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+package(default_visibility = ["//visibility:public"])
+
+load("@rules_pkg//:mappings.bzl", "pkg_filegroup")
+
+alias(
+    name = "dbscheme",
+    actual = "//cpp/ql/lib:dbscheme",
+)
+
+pkg_filegroup(
+    name = "db-files",
+    srcs = [
+        ":dbscheme",
+        "//cpp/downgrades",
+        "//cpp/ql/lib:dbscheme-stats",
+    ],
+)

cpp/BUILD.bazel

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+load("@rules_pkg//:mappings.bzl", "pkg_files", "strip_prefix")
+
+pkg_files(
+    name = "downgrades",
+    srcs = glob(
+        ["**"],
+        exclude = ["BUILD.bazel"],
+    ),
+    prefix = "cpp/downgrades",
+    strip_prefix = strip_prefix.from_pkg(),
+    visibility = ["//cpp:__pkg__"],
+)

cpp/downgrades/BUILD.bazel

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+package(default_visibility = ["//cpp:__pkg__"])
+
+load("@rules_pkg//:mappings.bzl", "pkg_files")
+
+pkg_files(
+    name = "dbscheme",
+    srcs = ["semmlecode.cpp.dbscheme"],
+    prefix = "cpp",
+)
+
+pkg_files(
+    name = "dbscheme-stats",
+    srcs = ["semmlecode.cpp.dbscheme.stats"],
+    prefix = "cpp",
+)