Flash option should look for output based on CMake target name

[noonfom]

Is your feature request related to a problem? Please describe.
Currently, the flash option looks in the build directory for foo.bin, where foo is the name of the project folder. On the other hand, the compile command outputs bar.bin, where bar is the name of the CMake target. However, it is not uncommon for developers to want to use a CMake target name different to the project folder name. This is especially true in the case of repositories containing multiple examples that share a common folder structure. In such circumstances, the flash option will fail as mbed-tools will not be able to locate the output binary.

Describe the solution you'd like
Consider looking for the output binary based on the CMake target name. This way the flash option can never fail.

Describe alternatives you've considered
Output the binary based on the project folder name.

Additional context
None.