Allow static Try*-like methods in patterns

[alrz]

This is a simpler approach to allow custom logic in patterns compared to #8613, as an advantage, this can work on any existing method that matches this signature.

return str.Split(':') switch {
    [double.TryParse(out var d), ..] =>  ...,
    [int.TryParse(out var i), ..] => ...,
}

This only affect exhaustiveness in terms of a binary match/fail output for each identical method,

return str.Split(':') switch {
    [double.TryParse(out 2.0), .. ] => ...,
    [double.TryParse(out 1.0), .. ] =>...,
}

This allows the compiler to generate a single double.TryParse call and then switching on the out variable value.

out prefix distinguishes between a "value" and a "pattern", because you may want to pass constant values to the method,

if (e is TryGet(1, 2, out { } x))
// ->
if (TryGet(e, 1, 2, out var x) && x is { })