RTOS : Add Message Pipe

[YarivCol]

Description

Message Pipe is FileHandle abstraction over rtos Mail.
It will be provide the user with ability to build more generic ITC or test code that use FileHandles

#5158 should be merged before this one.

[0xc0170]

cc @bulislaw @pan- @c1728p9

[pan-]

Thanks for splitting your previous PR into two distinct PRs.

[c1728p9]

This PR is mixing cmsis-os abstraction with mbed specific FileHandle code. Because of this it seems out of place in the rtos directory. It may be more appropriate to put this in features somewhere. What do you think?

CC @sg- @geky

[YarivCol]

@c1728p9 Every class in rtos folder depends on NonCopyable from mbed platform,I think its same case here too.

[pan-]

Sorry, I've approved the wrong PR, comments will follow.

[bulislaw]

I would say it would fit platform directory more, I would like to keep rtos directory with RTX primitives or thin utilities.
Also can you work on docs? Especially the overall description -> if I don't know anything and I read the class description I should understand what I can do with this class.
We would also like to have some unit tests for this PR.

[sg-]

Todo:

• links to API docs
• unit tests
  I get that it blurs RTOS and platform but Given this depends on RTOS, how does it not fit in the RTOS directory (if you remove RTOS is still works but otherwise you cant)? This would be the first RTOS tied change that I'm aware of platform directory.

[0xc0170]

@YarivCol Can you please respond to comments?

[YarivCol]

Yes, I will modify the docs and add unit test.
Working on it :) .

[0xc0170]

Yes, I will modify the docs and add unit test.

Let us know once done

[theotherjimmy]

@AnotherButler New API.

[mbed-ci]

Build : FAILURE

Build number : 85
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/5160/

[adbridge]

@YarivCol Any update on this ?

[0xc0170]

Please reopen once it is up to date with the changes requested above are answered.