Support enumerating binary suffixs for an extension

[zeroSteiner]

Support enumerating the extension suffixes for which a particular extension is available. This is foundational work that will allow Metasploit to suggest a Meterpreter that provides a particular extension.

Testing Steps

• Install the gem locally.
• Start msfconsole and then load IRB.
• Run `MetasploitPayloads.list_meterpreter_extension_suffixes('stdapi')
• See a list of Meterpreter extensions for Python, PHP, Java and 2 for Windows

Example

msf6 payload(python/meterpreter/reverse_tcp) > irb
[*] Starting IRB shell...
[*] You are in payload/python/meterpreter/reverse_tcp

>> MetasploitPayloads.list_meterpreter_extension_suffixes('stdapi')
=> ["php", "jar", "x64.dll", "py", "x86.dll"]

[gwillcox-r7]

Overall this looks very good but I did have some concerns r.e regex used here, a potential nil case that could be avoided, and some function naming concerns. Should all be pretty easy fixes though :)

[gwillcox-r7]

Correct me if I am wrong here but what happens if we push a nil entry into exts? Shouldn't this situation be avoided?

[zeroSteiner]

The conditional line is split across two lines, L133 won't be executed unless the conditions on L131 (::File.readable?(::File.join(root_dir, f))) and L132 (f =~ /#{EXTENSION_PREFIX}(\w+)\.#{binary_suffix}/) both evaluate to true at which point the group from the regex will be defined.

[gwillcox-r7]

Tests work as expected:

msf6 > irb
[*] Starting IRB shell...
[*] You are in the "framework" object

irb: warn: can't alias jobs from irb_jobs.
>> MetasploitPayloads.list_meterpreter_extension_suffixes('stdapi')
=> ["py", "x64.dll", "jar", "x86.dll", "php"]
>>