Document remaining features and components

[multiplemonomials]

Summary of changes

This PR finishes reorganizing and documenting Mbed's COMPONENTs and FEATUREs.

Impact of changes

• Fixes Redundant COMPONENT_FLASHIAP vs DEVICE_FLASH #230 (redundant COMPONENT_FLASHIAP)
• Partially addresses Linking netsocket pulls in too many dependencies #17 (Excessive dependencies of mbed-netsocket)
• Block device drivers will be available as CMake targets even without the relevant COMPONENT_xxx option declared in mbed_app.json now. The COMPONENT is still used to identify which dev boards they exist on by default, but now users won't have to mess with COMPONENTs just to make the driver available.
• COMPONENT_FLASHIAP removed, because I cannot see a reason for it to exist. Now, FlashIAPBlockDevice is available on all devices that have TARGET_FLASH (though you still need to link mbed-storage-flashiap to get access to it)
• Added COMPONENTs for all NFC drivers
• All COMPONENTs and FEATUREs now documented in features.json5!

Migration actions required

If user code was using the PN512 or M24SR drivers, the user will have to add the new COMPONENTs to get access to the drivers.

Documentation

(this is a mostly docs update)

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[X] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[X] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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