feat(rome_rowan): add a declare_union macro for one-off union AstNodes

[leops]

Summary

This PR add a new declare_union for creating union AST nodes scoped to a local module, without having to add them to js.ungram and rome_js_syntax. Its usage looks like the following example:

declare_union! {
    /// Documentation
    #[allow(dead_code)]
    pub(crate) UnionName = NodeType | OtherNodeType
}

The resulting union type is an enum with a variant for each node type in the union and implementing:

• the AstNode trait
• the Debug and Display traits
• the Clone, PartialEq, Eq and Hash traits with derive
• the From trait for each variants
• the Into trait for SyntaxNode and SyntaxElement

The macro is designed to fail to compile when the union would contain node types from different languages, as the AstNode trait must have a single Language associated type. I'm not really sure if and how this is a restriction we may lift in the future.

Test Plan

This macro is now used to implement the JsAnyBinaryLikeExpression and JsAnyBinaryLikeLeftExpression types in the formatting of binary-like expressions

[github-actions]

Playground for commit f50bc64

[github-actions]

Parser conformance results on ubuntu-latest

js/262

Test result	main count	This PR count	Difference
Total	45878	45878	0
Passed	44938	44938	0
Failed	940	940	0
Panics	0	0	0
Coverage	97.95%	97.95%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	39	39	0
Passed	36	36	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.31%	92.31%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	5946	5946	0
Passed	350	350	0
Failed	5595	5596	❌ ⏫ +1
Panics	1	0	✅ ⏬ -1
Coverage	5.89%	5.89%	0.00%

⁉️ Panic To Failed (1):

typeGuardsAsAssertions.symbols

ts/babel

Test result	main count	This PR count	Difference
Total	588	588	0
Passed	519	519	0
Failed	69	69	0
Panics	0	0	0
Coverage	88.27%	88.27%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	16257	16257	0
Passed	12391	12391	0
Failed	3866	3866	0
Panics	0	0	0
Coverage	76.22%	76.22%	0.00%

[ematipico]

nit: could we call declare_language_union or declare_node_union (this is maybe better, because it applies AstNode)?

The name, right now, is so generic that we could misuse it.

[leops]

I'll change it to declare_node_union, I also think it's the better option since the type being declared and all the types it contains must be AST nodes

[ematipico]

Sorry I can't really understand the purpose of this macro. Could you explain please?

[leops]

This macro is an implementation detail of declare_union (it's not exported from the macros module) aimed at making it easier to implement the UnionLanguage trait. This trait is implemented for tuples of various arity, but because tuples are heterogeneous the implementation needs to declare one generic type for each element of the tuple. This in turn means it's impossible to implement the trait once for all tuples size, instead implementing the trait would look like this:

impl<T1> UnionLanguage for (T1,) { ... }
impl<T1, T2> UnionLanguage for (T1, T2) { ... }
impl<T1, T2, T3> UnionLanguage for (T1, T2, T3) { ... }

All these impl blocks share the same code with the only difference being the number of generic types, so it was simpler to write that code in a macro so it can easily be repeated for various numbers of generic arguments

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