[REPL] Autocompletion of kwargs for some common functions no longer works

[mbauman]

In 1.10.7 and 1.11.2, one could autocomplete, for example, using DataFrames; show(df, allrTAB and get show(df, allrows=. This no longer works on 1.10.9 and 1.11.4.

Kwarg completions on functions with more than 40 methods was subsequently disabled due to #54131. But that case is quite extreme! An MWE here that emulates what PyCall is doing is:

struct F; end
Base.getproperty(::F, ::Symbol) = Any[cos, sin][rand(1:2)]
f = F()
f.bar(<TAB>

In short, this asks for tab completion on (::Any)(...) — that is, every method in the system! All 30k+ of them. So, yeah, that's gonna be sluggish.

The fix in #56963 used MAX_METHOD_COMPLETIONS to limit this. That's set to 40, based upon a display limitation. I think it'd be reasonable to increase this to something like 500, which would cover nearly all functions. In the examples above, finding the allrows kwarg for show — which has 304 methods with DF.jl loaded on 1.11.2 — has no noticeable latency.

Could we increase the limit here?