Generate Plugin.cs for C#
This used to be infeasible as we didn't expose the descriptor protos, but it's fine now.
Tested against https://github.com/googleapis/gapic-generator-csharp by removing the local version there.
Fixes #5007.
diff --git a/csharp/generate_protos.sh b/csharp/generate_protos.sh
index b021de2..62ba1a1 100755
--- a/csharp/generate_protos.sh
+++ b/csharp/generate_protos.sh
@@ -40,7 +40,8 @@
src/google/protobuf/struct.proto \
src/google/protobuf/timestamp.proto \
src/google/protobuf/type.proto \
- src/google/protobuf/wrappers.proto
+ src/google/protobuf/wrappers.proto \
+ src/google/protobuf/compiler/plugin.proto
# Test protos
# Note that this deliberately does *not* include old_extensions1.proto
