Add modern C++ language feature support to syntax highlighting

[shavesha]

This commit updates the C++ syntax highlight rules to support:

• C++20 features: concepts, consteval, constinit, coroutines (co_await, co_yield, co_return)
• Modules support (import, module)
• Extended preprocessor directives (__has_include, __has_embed, etc.)
• Additional control flow directives (elifdef, elifndef)
• Newer type support (char8_t)
• Contract programming keywords (pre, post, contract_assert)

These changes ensure proper syntax highlighting for modern C++ codebases using recent language standards.

Issue #, if available:

Description of changes:

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Pull Request Checklist:

• No backwards incompatible changes were made to Ace's public interface which is defined through the main typings file (ace.d.ts) and its references:
  • https://github.com/ajaxorg/ace/blob/master/ace.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-modes.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-extensions.d.ts

[xyos]

@shavesha can you take a look at the failing tests?