Individual libraries' `target_h` stub headers have now all been moved
from `mbed-headers-base` to `mbed-headers-<library>`.
Note: Even though headers previously in `target_h` are technically
stubs/fakes too, they are used by not only unit tests but also regular
libraries when compiled for unit tests, because no target-specific HAL
implementation exists in this case. In order for regular library
sources to pick up `target_h` headers, those headers must
* have the same names as regular headers
* appear first in include paths
This is why those headers are part of `mbed-headers-<library>` and not
`mbed-stubs-<library>`. Before this refactoring, `mbed-headers-base`
was the first in unit tests' include paths.
Previously the drivers stub library depended on `mbed-headers`, which
is a collection of all available headers in mbed-os. To make it easier
to separate the library, only depend on the headers we're using.
Move the header-only mbed-headers-drivers library the unit test stubs
depend on into the drivers component directory. This makes the drivers
stubs more self-contained and improves the composition of the library.
Lingkai Dong
Rajkumar Kanagaraj