feat: Support multi-version generation

This allows the generator repo to be imported multiple times with
different versions, so the same Bazel workspace can have different
APIs generated with different versions.

repositories.bzl

@@ -16,7 +16,7 @@ load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 load("//rules_csharp_gapic:csharp_compiler_repo.bzl", "csharp_compiler", "dotnet_restore")
 
-def gapic_generator_csharp_repositories():
+def gapic_generator_csharp_repositories(gapic_generator_suffix = ""):
     _rules_gapic_version = "0.8.0"
     _rules_gapic_sha256 = "75705d03068ba07cc885a85bb4585e2a278414e31510e60577df8437a28a4ae1"
 
@@ -34,6 +34,6 @@ def gapic_generator_csharp_repositories():
     )
     maybe(
         dotnet_restore,
-        name = "gapic_generator_restore",
-        csproj = "@gapic_generator_csharp//:Google.Api.Generator/Google.Api.Generator.csproj",
+        name = "gapic_generator_restore%s" % gapic_generator_suffix,
+        csproj = "@gapic_generator_csharp%s//:Google.Api.Generator/Google.Api.Generator.csproj" % gapic_generator_suffix,
     )

rules_csharp_gapic/csharp_gapic.bzl

@@ -41,6 +41,7 @@ def csharp_gapic_library(
         grpc_service_config = None,
         common_resources_config = None,
         service_yaml = None,
+        generator_binary = "//rules_csharp_gapic:csharp_gapic_generator_binary",
         **kwargs):
     # Build zip file of gapic-generator output
     name_srcjar = "{name}_srcjar".format(name = name)
@@ -54,7 +55,7 @@ def csharp_gapic_library(
     proto_custom_library(
         name = name_srcjar,
         deps = srcs,
-        plugin = Label("//rules_csharp_gapic:csharp_gapic_generator_binary"),
+        plugin = Label(generator_binary),
         plugin_file_args = plugin_file_args,
         output_type = "gapic",
         output_suffix = ".srcjar",