Update Kotlin compiler to escape package names (#13310)

The current Kotlin code generator creates code which fails to compile with imports like:

```
syntax = "proto3";
package net.example.v1;
message Sample {
  string net = 1;
}
```

This results in a condition where 'net' is ambiguous in some cases (could refer to the field or the package). To avoid these issues, the code generator should enclose package paths in backticks:

```
net.example.v1.SampleKt => `net.example.v1`.SampleKt
```

Fixes #13182.

Closes #13310

COPYBARA_INTEGRATE_REVIEW=#13310 from pkwarren:pkw/issue-13182 3f72b2f
PiperOrigin-RevId: 564481691

Author: pkwarren

src/google/protobuf/compiler/java/message.cc

@@ -1316,8 +1316,7 @@ void ImmutableMessageGenerator::GenerateTopLevelKotlinMembers(
       "message",
       EscapeKotlinKeywords(name_resolver_->GetClassName(descriptor_, true)),
       "message_kt",
-      EscapeKotlinKeywords(
-          name_resolver_->GetKotlinExtensionsClassName(descriptor_)));
+      name_resolver_->GetKotlinExtensionsClassNameEscaped(descriptor_));
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     if (IsMapEntry(descriptor_->nested_type(i))) continue;

src/google/protobuf/compiler/java/message_lite.cc

@@ -841,8 +841,7 @@ void ImmutableMessageLiteGenerator::GenerateTopLevelKotlinMembers(
       "message",
       EscapeKotlinKeywords(name_resolver_->GetClassName(descriptor_, true)),
       "message_kt",
-      EscapeKotlinKeywords(
-          name_resolver_->GetKotlinExtensionsClassName(descriptor_)));
+      name_resolver_->GetKotlinExtensionsClassNameEscaped(descriptor_));
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     if (IsMapEntry(descriptor_->nested_type(i))) continue;
@@ -853,7 +852,8 @@ void ImmutableMessageLiteGenerator::GenerateTopLevelKotlinMembers(
   GenerateKotlinOrNull(printer);
 }
 
-void ImmutableMessageLiteGenerator::GenerateKotlinOrNull(io::Printer* printer) const {
+void ImmutableMessageLiteGenerator::GenerateKotlinOrNull(
+    io::Printer* printer) const {
   // Generate getFieldOrNull getters for all optional message fields.
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);

src/google/protobuf/compiler/java/name_resolver.cc

@@ -342,6 +342,21 @@ std::string ClassNameResolver::GetKotlinExtensionsClassName(
                           descriptor->file(), true, true, true);
 }
 
+std::string ClassNameResolver::GetKotlinExtensionsClassNameEscaped(
+    const Descriptor* descriptor) {
+  std::string name_without_package = ClassNameWithoutPackageKotlin(descriptor);
+  std::string full_name = GetClassFullName(
+      name_without_package, descriptor->file(), true, true, true);
+  std::string name_without_package_suffix =
+      absl::StrCat(".", name_without_package, "Kt");
+  size_t package_end = full_name.rfind(name_without_package_suffix);
+  if (package_end != std::string::npos) {
+    return absl::StrCat("`", full_name.substr(0, package_end), "`",
+                        name_without_package_suffix);
+  }
+  return full_name;
+}
+
 std::string ClassNameResolver::GetJavaMutableClassName(
     const Descriptor* descriptor) {
   return GetJavaClassFullName(ClassNameWithoutPackage(descriptor, false),

src/google/protobuf/compiler/java/name_resolver.h

@@ -102,6 +102,7 @@ class ClassNameResolver {
   std::string GetJavaImmutableClassName(const ServiceDescriptor* descriptor);
   std::string GetKotlinFactoryName(const Descriptor* descriptor);
   std::string GetKotlinExtensionsClassName(const Descriptor* descriptor);
+  std::string GetKotlinExtensionsClassNameEscaped(const Descriptor* descriptor);
   std::string GetJavaMutableClassName(const Descriptor* descriptor);
   std::string GetJavaMutableClassName(const EnumDescriptor* descriptor);
   std::string GetJavaMutableClassName(const ServiceDescriptor* descriptor);