Make enum trait a list of structures

[mtdowling]

The enum trait is currently a map of enum value to the enum definition.
This means that models often look like this:

@enum(foo: {}, bar: {})
string MyString

Ideally, a name and documentation are provided too:

@enum(
    foo: {name: "FOO", documentation: "foo docs..."},
    bar: {name: "BAR", documentation: "bar docs..."})

However, the difference between the key and "name" has resulted in
confusion as to which is which. This is caused by a couple things:

1. The key doesn't tell you what it defines. You have to know that the
   the key defines the value of the enum to make sense of the trait.
2. The key has to be quoted if it deviates from the allows ABNF for node
   object keys. This has also led to confusion.

Although this is a breaking change, using a list of structures where
everything has a name will result in models that are easier to
understand, and hopefully modelers will more often include properties
like name and documentation.

This now looks like:

@enum([
    {
        value: "foo",
        name: "FOO",
        documentation: "foo docs..."
    },
    {
        value: "bar",
        name: "BAR",
        documentation: "bar docs..."
    }
])

Issue #, if available:

Description of changes:

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