Fix tools discovery by strictly following json data when available

[cmaglie]

Should fix #5042 and #5168.

(in particular #5168 would need more work to implement my proposal of coreDependencies field into package_index.json to be a complete solution, IMHO)

See also #5197.

/cc @facchinm @PaulStoffregen @matthijskooijman @per1234 @jantje

[ArduinoBot]

✅ Build completed.

Please test this code using one of the following:

⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-5199-BUILD-584-linux32.tar.xz
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-5199-BUILD-584-linux64.tar.xz
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-5199-BUILD-584-windows.zip
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-5199-BUILD-584-macosx.zip
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-5199-BUILD-584-linuxarm.tar.xz

ℹ️ The linuxarm build is still experimental and may not be always available.

[per1234]

I tested build 584 with the following URLs:
https://raw.githubusercontent.com/MCUdude/MightyCore/b3d9b22f15ec98e5c4ab54741357b941a8338c73/package_MCUdude_MightyCore_index.json

• toolsDependencies: none
• tools: none

https://raw.githubusercontent.com/MCUdude/MightyCore/496567391dc35d756e7b8a3f06bce830e8e77131/package_MCUdude_MightyCore_index.json

• toolsDependencies:
  • avr-gcc 4.8.1-arduino5
  • avrdude 6.0.1-arduino5
• tools: none

https://raw.githubusercontent.com/per1234/MightyCore/update-tools-dependencies/package_MCUdude_MightyCore_index.json

• toolsDependencies:
  • avr-gcc 4.9.2-atmel3.5.3-arduino2
  • avrdude 6.3.0-arduino2
• tools: none

https://raw.githubusercontent.com/per1234/MightyCore/add-tools/package_MCUdude_MightyCore_index.json

• toolsDependencies:
  • avr-gcc-MightyCore 4.8.1-arduino5
  • avrdude-MightyCore 6.0.1-arduino5
• tools(given unique names to avoid Arduino IDE selects wrong board package toolchain #5042 in previous IDE versions):
  • avr-gcc-MightyCore 4.8.1-arduino5
  • avrdude-MightyCore 6.0.1-arduino5

https://raw.githubusercontent.com/per1234/MightyCore/add-old-tools/package_MCUdude_MightyCore_index.json

• toolsDependencies:
  • avr-gcc 4.8.1-arduino5
  • avrdude 6.0.1-arduino5
• tools:
  • avr-gcc 4.8.1-arduino5
  • avrdude 6.0.1-arduino5

https://raw.githubusercontent.com/per1234/MightyCore/add-new-tools/package_MCUdude_MightyCore_index.json

• toolsDependencies:
  • avr-gcc 4.9.2-atmel3.5.3-arduino2
  • avrdude 6.3.0-arduino2
• tools:
  • avr-gcc 4.9.2-atmel3.5.3-arduino2
  • avrdude 6.3.0-arduino2

In all cases the installation proceeded correctly. When the specified tool version was already installed that copy was used. The correct tools were selected for compilation, upload, and Burn Bootloader with MightyCore and Arduino AVR Boards. When a core was updated with a new tool version if the previous tool version was referenced it was left installed, otherwise it was removed.