Slow local variables load in VSCode due to inspect of large variables #674

Your environment

• ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux-gnu]
• rdbg commit b8f799f from master

Describe the bug
VSCode is very slow to load the local variables window in my app when it stops at a breakpoint where the self object has an instance variable of type RubyXL::Worksheet (with images in it) as well as an instance variable for the parent workbook in the self because the obj.inspect in rdbg's safe_inspect is returning a very large string. See also #635 (comment) where the obj.inspect for a worksheet in the backtrace was taking nine or ten minutes to return a 16 MB string, and the comments at #635 (comment) and after.

I am running the debugger in a WSL instance, so this might be slowing things down more than running it natively.

Expected behavior
VSCode should be able to load the local variables window in a reasonable time (preferably micro or milliseconds) rather than freezing.

Additional context
One solution is to use the same fix as for #635 by using the LimitedPP.pp call instead of obj.inspect in safe_inspect, eg:

 def self.safe_inspect obj, max_length: SHORT_INSPECT_LENGTH, short: false
    if short
      LimitedPP.pp(obj, max_length)
    else
      #obj.inspect
      LimitedPP.pp(obj, 32768)
    end

With this change, the local variables window loads in VSCode in a reasonable time.

I tried using a limit of up to 128 kB and the local variables window is noticeably slow to load but still of the order of a second.