Use extern "C" to remove C++ name mangling

[doingnz]

Description

Apply extern "C" {...} at the .h or top of C/CPP files, not around method bodies.
Remove methods with appendied "_C" after applying extern "C" to function prototype.

Motivation and Context

Remove redundant "_C" method calls to avoid speed penalty on methods called often.
Small space saving and less methods to maintain.

How Has This Been Tested?

Build ESP32 and STM32 sample projects.

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (work on Unit Tests, has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[nfbot]

Hi @doingnz,

I'm nanoFramework bot.
Thank you for your contribution!

A human will be reviewing it shortly. 😉

[nfbot]

@doingnz there are issues with the code style on the source files.
A PR was submitted with the code style fixes. Please click doingnz#13, review the changes if you want and merge it.

Make sure to follow the project code style. Check the details here on how it works and the tools required to help you with that.

[josesimoes]

@doingnz please merge the PR with the code style fixes 😉

[josesimoes]

LGTM! Nice improvement. 👏🏻