envoy_cc_library: add export of foo_with_external_headers (#8005)

Add a parallel native.cc_library to envoy_cc_library
for external projects that consume Envoy's libraries. This allows the consuming
project to disambiguate overlapping include paths when repository overlaying is used,
as it can now include envoy headers via external/envoy/...

Risk Level: Low
Testing: N/A

Signed-off-by: Otto van der Schaaf <[email protected]>

bazel/envoy_library.bzl

@@ -70,6 +70,17 @@ def envoy_cc_library(
         strip_include_prefix = strip_include_prefix,
     )
 
+    # Intended for usage by external consumers. This allows them to disambiguate
+    # include paths via `external/envoy...`
+    native.cc_library(
+        name = name + "_with_external_headers",
+        hdrs = hdrs,
+        copts = envoy_copts(repository) + copts,
+        visibility = visibility,
+        deps = [":" + name],
+        strip_include_prefix = strip_include_prefix,
+    )
+
 # Used to specify a library that only builds on POSIX
 def envoy_cc_posix_library(name, srcs = [], hdrs = [], **kargs):
     envoy_cc_library(