sdbus++: async: client: make methods snake_case to match server

Use snake_case in generated bindings to match the server bindings
naming convention.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I17c89a2e85cd4906bbfe1eaab86ab0b1837aad88
diff --git a/example/calculator-client.cpp b/example/calculator-client.cpp
index ab47767..2db6ae2 100644
--- a/example/calculator-client.cpp
+++ b/example/calculator-client.cpp
@@ -28,7 +28,7 @@
 
     {
         // Get the LastResult property.
-        auto _ = co_await c.lastResult();
+        auto _ = co_await c.last_result();
         std::cout << "Should be 42: " << _ << std::endl;
     }
 
@@ -39,15 +39,15 @@
 
     {
         // Get the LastResult property.
-        auto _ = co_await c.lastResult();
+        auto _ = co_await c.last_result();
         std::cout << "Should be 0: " << _ << std::endl;
     }
 
     {
         // Set the LastResult property.
-        co_await c.lastResult(1234);
+        co_await c.last_result(1234);
         // Get the LastResult property.
-        auto _ = co_await c.lastResult();
+        auto _ = co_await c.last_result();
         std::cout << "Should be 1234: " << _ << std::endl;
     }