Add specifier to generated tool property keys

[facchinm]

port of arduino/Arduino#4795 to golang
should solve arduino/Arduino#5042

This is far less powerful than Java version since the tools are not tangled with json package_index but all the information are extracted from the folder name.
Since the folder name only has a "vendor" subpath we cannot correlate the tools with the required version but only try to match the architecture being compiled with the tool vendor.

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/arduino-builder/arduino-builder-165.zip

ℹ️ To test this build:

1. Replace arduino-builder binary (you can find it where you installed the IDE) with the provided one

[agdl]

👍 Working with red bear labs hardware installed!

[facchinm]

This PR breaks 4 tests (TestSetupBuildProperties, TestSetupBuildPropertiesWithMissingPropsFromParentPlatformTxtFiles, TestLoadTools, TestLoadLotsOfTools).
They are not really "broken" but the folder structure of downloaded_tools doesn't match board manager's so the builtin tools are now "visible", while they were hidden by downloaded_tools before.
This could be a problem when updating AVR core with new tools (arduino/Arduino#5021) on older IDEs

@matthijskooijman @cmaglie , any idea on how we can solve this in a sane way (without parsing package_index json, which would be the best option in the long term)?

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/arduino-builder/arduino-builder-165.zip

ℹ️ To test this build:

1. Replace arduino-builder binary (you can find it where you installed the IDE) with the provided one

[facchinm]

Superseded by arduino/Arduino#5199