[Macros] Copy attrs/modifiers on MacroExpansionDecl to expanded decls

[rintaro]

As per the SE-0397 amendment, copy attributes and modifiers on MacroExpansionDecl to the expanded declarations.

Preparation:

• Rename AttributedSyntax to WithAttributesSyntax.
• Keep AttributedSyntax as a typealias to WithAttributeSyntax
• Introduce WithModifiersSyntax
• Add init(_: [Element]) to SyntaxCollection's requirements

[rintaro]

@swift-ci Please test

[rintaro]

Oh this is now unrelated to this PR. I wanted to use this feature (representedLiteralValue ) in swift repo test cases, but ended up with not using it because the compiler doesn't support @freestanding(declaration, names: arbitrary) macros.

But this was missing anyway.

[ahoppen]

Thanks for noticing and fixing 🙏🏽

[ahoppen]

Thanks for noticing and fixing 🙏🏽

[ahoppen]

As with my comment in your other PR, I would really prefer this to be three different assertMacroExpansion calls, each only having a single #decl macro expansion. It just makes debugging so much easier if the test case fails.

Test 1

struct S {
  public #decls(
    """
    static func foo() {
    print("value") }
    """,
    "struct Inner {\n\n}"
  )
}

Test 2

struct S {
  @attr static #decls("var value1 = 1", "typealias A = B")
}

Test 3

@attribute
@otherAttribute(x: 1) #decls("@moreAttibute var global = 42")

[rintaro]

@swift-ci Please test

[rintaro]

@swift-ci Please test Windows