Some Method objects use wrong .gist method

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Migrated from rt.perl.org#132149 (status was 'new')

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[p6rt]

From @zoffixznet

Method objects have their own `.gist` method[^1] that just print `.name`. However, under some
circumstances, that method is lost, and `Mu​::gist` is used instead​:

  <Zoffix__> m​: <z>.comb.^methods.grep(*.name eq 'eager').say
  <camelia> rakudo-moar 7af339​: OUTPUT​: «(Method+{<anon|61058032>}.new)␤»

I tried to fix it and failed, but found some facts about the bug that might give a hint​:

*) The problematic methods has `is nodal` trait on them (which mixes in a role), but NOT all nodal
  methods have this issue
*) (90% sure this is what happened) If you add an only `method z is nodal {}` to src/core/Any.pm, the bug doesn't appear
*) If you add a `multi method z is nodal {}` to src/core/Any.pm the bug occurs
*) If you do the same thing with a regular class, it doesn't happen. BTW​: `Any` is augmented in core
*) .file on the method gives src/core/Method.pm. However, if you modify Mu.gist to append some string,
  you'll see that it's Mu's method that gets called.

  <Zoffix__> m​: my $m = <z>.comb.^methods.grep(*.name eq 'eager').head; dd $m.^lookup('gist').cando(\($m)).head.file
  <camelia> rakudo-moar 7af339​: OUTPUT​: «"SETTING​::src/core/Method.pm"␤»

*) Even if you make Method.gist an `only` method, the Mu​::gist one is still the one that gets called
*) If you implement only or multi method `gist` in the role that `is nodal` mixed in[^2], trying to
  call .gist on the buggy method gives "Cannot invoke this object (REPR​: Null; VMNull)"

[1] https://github.com/rakudo/rakudo/blob/045ef448b62c045630abb8e167cc45d1f9fe6902/src/core/Method.pm#L4
[2] https://github.com/rakudo/rakudo/blob/7af339b91d2a56a4a4eb065952cd548c188bd124/src/core/traits.pm#L357