system_config.rb: refactor code into worker functions

[maxim-belkin]

This PR breaks down dump_verbose_config function into "worker" functions that display information for specific categories:

• core_tap_config for Core tap info
• homebrew_config for Homebrew/brew info
• homebrew_env_config for environment-related information
• host_software_config for Host software

Also, I factored out code related to Clang into a new describe_clang function, so that we can do:

f.puts "Clang: #{describe_clang}"

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[MikeMcQuaid]

Nice cleanup.

[maxim-belkin]

Nice cleanup.

Thank you! :)