[Feature request] Better semantics for try/catch

Note: this is a breaking change!

I would like to see the semantics of try/catch be changed to make it (in my opinion) more useful.

I think that

x = try
    do_something()
catch err
    handle_error(err)

should be changed from compiling to

local x = xpcall(function()
    return do_something()
end, function(err)
    return handle_error(err)
end)

into compiling to this:

local x = select(2, xpcall(function()
    return do_something()
end, function(err)
    return handle_error(err)
end))

The addition of select(2, [...]) causes the boolean that's normally returned by xpcall() to be skipped. This would feel more natural to use in many cases, and allow for patterns like this:

x = (try maybe_failing_operation()) ?? "default"

Start by locating the compiler handling try/catch and the existing xpcall lowering, then compare its generated Lua with the examples in this issue. Done means the proposed result-handling semantics are implemented consistently, including the default-value pattern, with coverage for the breaking behavior.