fix(frontends/lean/definition_cmds): export `using_well_founded` AST node (#784)
fix(frontends/lean/definition_cmds): export `using_well_founded` AST node (#784)

Turns out that the ast.json export has been broken this whole time in ignoring definitions which use `using_well_founded`. cc: @gebner , can we get a point release out with this bugfix?



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