Simplify C++ TM struct generation (facebook#3947)

Update documentation to match:
facebook/react-native#41645

Author: christophpurrer

docs/the-new-architecture/cxx-custom-types.md

@@ -257,10 +257,10 @@ This works - but is quite complex.
 [**Codegen**](pillars-codegen.md) for C++ Turbo Native Modules does support struct generators, so you can simplify the code above in `NativeSampleModule.h` to:
 
 ```cpp
-using CustomType = NativeSampleModuleBaseCustomType<std::string, bool, std::optional<int32_t>>;
+using CustomType = NativeSampleModuleCustomType<std::string, bool, std::optional<int32_t>>;
 template <>
 struct Bridging<CustomType>
-    : NativeSampleModuleBaseCustomTypeBridging<std::string, bool, std::optional<int32_t>> {};
+    : NativeSampleModuleCustomTypeBridging<CustomType> {};
 ```
 
 With `using CustomType` you declare a name for your concrete struct.
@@ -276,10 +276,9 @@ Without any custom conversion functions:
 
 #### Base class
 
-`NativeSampleModuleBaseCustomType` is an auto-generated template in your `AppSpecsJSI.h` which name is generated by:
+`NativeSampleModuleCustomType` is an auto-generated template in your `AppSpecsJSI.h` which name is generated by:
 
 - `NativeSampleModule` (name of C++ Turbo Native Module in the JavaScript spec) +
-- `Base` (constant) +
 - `CustomType` (name of type in the JavaScript spec)
 
 The same naming schema applies to the necessary `Bridging` struct which is defined via `struct Bridging<CustomType>`.