Add macro declaration syntax.

[gilbens-starkware]

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[reviewable-StarkWare]

This change is 

[orizi]

Reviewed 8 of 14 files at r1, 1 of 2 files at r2, all commit messages.
Reviewable status: 9 of 15 files reviewed, 2 unresolved discussions (waiting on @gilbens-starkware)

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crates/cairo-lang-parser/src/parser.rs line 1487 at r2 (raw file):

            SyntaxKind::TerminalDiv => self.take::<TerminalDiv>().into(),
            SyntaxKind::TerminalDivEq => self.take::<TerminalDivEq>().into(),
            SyntaxKind::TerminalDollar => self.take::<TerminalDollar>().into(),

should dollar be not fully part of the identifier?

Code quote:

            SyntaxKind::TerminalDollar => self.take::<TerminalDollar>().into(),

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crates/cairo-lang-parser/src/parser.rs line 1861 at r2 (raw file):

    /// Parses an expr block, while allowing placeholder expressions. Restores the previous
    /// placeholder expression setting after parsing.
    fn parse_block_with_placeholders(&mut self) -> ExprBlockGreen {

doesn't this have exactly a single caller?

Code quote:

 parse_block_with_placeholders(