Platforms installed in the sketchbook/user dir should have priority

[cmaglie]

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Describe the problem

A platform installed in the sketchbook/user directory under the hardware folder should take priority over another platform with matching VENDOR and ARCHITECTURE installed via Board Manager, and this is currently not happening.

The documentation should reflect this behavior.

/cc @thernstig

To reproduce

This is an example for Linux, but it can be easily adapted for other OS:

$ arduino-cli core install arduino:[email protected]
[...]
$ mkdir -p ~/Arduino/hardware/arduino/
$ cp -a ~/.arduino15/packages/arduino/hardware/samd/1.8.13 ~/Arduino/hardware/arduino/samd
$ arduino-cli core install arduino:[email protected]
$ arduino-cli core list | grep samd
arduino:samd             1.8.14           1.8.14           Arduino SAMD Boards (32-bits ARM Cortex-M0+)

Expected behavior

The version displayed is 1.8.14 but it should be 1.8.13 since it's the one loaded in the sketchbook.

Arduino CLI version

nightly

Operating system

N/A

Operating system version

N/A

Additional context

No response

Issue checklist

• [x] I searched for previous reports in the issue tracker
• [x] I verified the problem still occurs when using the nightly build
• [x] My report contains all necessary details