Migrate codebase to use S2N_RESULT by default

[camshaft]

Problem:

Right now, most of the codebase uses int as the function return value. As documented in s2n_result.c, this has a few problems:

• GUARDing in a function that returns integer types
• GUARDing a function that returns integer type
• Forgetting to GUARD a function that returned an error signal

Solution:

The majority of the codebase should return S2N_RESULT. This is statically checked to ensure:

• The code cannot GUARD in a function that returns integer types:

  uint8_t s2n_answer_to_the_ultimate_question() {
    GUARD(s2n_sleep_for_years(7500000)); /* <- Won't compile since this function doesn't return an S2N_RESULT */
    return 42;
  }

• The code cannot GUARD a function that returns integer types:

  S2N_RESULT s2n_deep_thought() {
    GUARD(s2n_answer_to_the_ultimate_question()); /* <- Won't compile since the function being called doesn't return an S2N_RESULT */
    return S2N_RESULT_OK;
  }

• The code cannot ignore the return value of a function

  uint8_t s2n_answer_to_the_ultimate_question() {
    s2n_sleep_for_years(7500000); /* <- Won't compile since the function being called returns a `S2N_RESULT` isn't `GUARD`ed */
    return 42;
  }

Requirements / Acceptance Criteria:

The following tasks are implemented in a way that will make the transition as painless as possible, especially for any pending PRs.

• Implement S2N_RESULT utils: add s2n_result implementation #1872
• Add a codegen script to consistently generate safety macros for all function contexts utils: add safety_macros codegen script #2423
• Add a codemod script to migrate all of the existing code to use the new naming convention utils: add safety codemod script #2339
• Implement a GitHub Action to ensure the s2n_safety_macros.h is only modified through the codegen script. (see utils: add safety_macros codegen script #2423 (comment))
• Add a S2N_RESULT_FREE return type that is allowed to be used in the DEFER_CLEANUP macro. Fix and simplify psk_param lifecycle #2523
• Apply the codemod script to main and existing PRs utils: apply safety macro codemod script #2441
• Remove the old safety macros, since the codemod has been applied and none of the code is using the old macros anymore. utils: remove deprecated safety macros #2747
• Update the safety macros codegen script to add prefix-less set of macros by duplicating all of the RESULT_ declarations. This means that RESULT_GUARD is now just GUARD.
• Add a codemod script to move all of the RESULT_ invocations in the codebase, since it's now the default.
• Manually update all of the functions in the codebase to return S2N_RESULT instead of int (see utils: continued result migration #1891 Add S2N_RESULT to a couple functions. #2371)
  This can be done per module and replacing all of the int with S2N_RESULT and trying to compile it. After working through all of the compiler issues, that module should continue to have the same functionality with the added guarantees that S2N_RESULT provides.
• Improve comparison macros to ensure values have the same type before comparing