bazel: Add initial config for binary distribution (see #3757)

Add support for building the CEF binary distribution using Bazel
and the default platform toolchain. Tested to work for Windows
x64, MacOS ARM64 and x64 (cross-compile from ARM64), and
Linux x64. Windows x86 (cross-compile from x64) is known to
be broken, see https://github.com/bazelbuild/bazel/issues/22164.

Includes minor changes to tests directory structure to meet
Bazel build requirements.

bazel/linux/fix_rpath.bzl

@@ -0,0 +1,41 @@
+# Copyright (c) 2024 The Chromium Embedded Framework Authors. All rights
+# reserved. Use of this source code is governed by a BSD-style license that
+# can be found in the LICENSE file.
+
+def _fix_rpath_impl(ctx):
+    inputs = ctx.runfiles(files = [ctx.file.src])
+    # Bring over 'data' dependencies from the input.
+    inputs = inputs.merge_all([ctx.attr.src[DefaultInfo].default_runfiles])
+
+    src = ctx.file.src.path
+    out = ctx.outputs.out.path
+
+    ctx.actions.run_shell(
+        outputs = [ctx.outputs.out],
+        inputs = inputs.files,
+        arguments = [src, out],
+        command = "cp $1 $2 && " +
+                  "chmod +w $2 && " +
+                  "patchelf --remove-rpath $2 && " +
+                  "patchelf --set-rpath '$ORIGIN' $2"
+    )
+
+    return [DefaultInfo(files = depset([ctx.outputs.out]))]
+
+# Set rpath to $ORIGIN so that libraries can be loaded from next to the
+# executable. The result can be confirmed with:
+# $ objdump -x ./bazel-bin/path/to/binary | grep 'R.*PATH'
+#
+# Alternatively, define a custom CC toolchain that overrides
+# 'runtime_library_search_directories'.
+#
+# This rule requires preinstallation of the patchelf package:
+# $ sudo apt install patchelf
+fix_rpath = rule(
+    implementation = _fix_rpath_impl,
+    attrs = {
+        "src": attr.label(allow_single_file = True),
+        "out": attr.output(mandatory = True),
+    },
+)
+