Fix: Add turbofish support to bsn!

[Tatsuya0330]

Objective

• Fixes Turbofish is not supported in bsn! #24962

Background

• Previously, when calling a template constructor within the bsn! with turbofish syntax, the generic type arguments were completely omitted upon macro expansion.
• This happened because TemplateConstructor and FromTemplateConstructor did not possess any variables or fields designated to receive and output those type arguments.

Solution

crates/bevy_scene/macros/src/bsn/types.rs

• Added a pub function_generics: Option<syn::AngleBracketedGenericArguments> field to the BsnConstructor struct.

crates/bevy_scene/macros/src/bsn/parse.rs

• I extended take_last_path_ident and introduced a new function.
  • take_last_path_segment: which retrieves a syn::PathSegment containing both the identifier and the arguments.
• During the parsing of PathType::TypeFunction, the generic arguments enclosed in angle brackets following the method name are now extracted.
  • Stored in a newly added field, function_generics, within BsnConstructor.

crates/bevy_scene/macros/src/bsn/codegen.rs

• Added logic to expand the extracted function_generics as a turbofish immediately after the method name during token generation for TemplateConstructor and FromTemplateConstructor.

Testing

Added unit test

• Verified that the turbofish is correctly token-expanded in TemplateConstructor and FromTemplateConstructor.