JS AST templating and matching

[knutwannheden]

This PR introduces a new templating system that provides a clean, TypeScript-friendly API for JavaScript AST pattern matching and code generation using tagged template literals.

pattern() - Pattern Matching

Create patterns to match against AST nodes and extract matched captures:

const addPattern = pattern`${"left"} + ${"right"}`;

const match = await addPattern.match(expression);
if (match) {
   const leftOperand = match.get("left");
   const rightOperand = match.get("right");
}

template() - AST Generation

Generate new AST nodes from templates:

// Direct value substitution
const newNode = template`${rightOperand} + ${leftOperand}`.apply(cursor, expression);

// Mix of captures, AST nodes, and primitives
const result = template`if (${condition}) return ${42};`.apply(cursor, statement);

capture() - Reusable Placeholders

Create placeholders for pattern matching and value reuse:

const expr = capture();

// Use same capture multiple times when requiring subtrees to be identical
const redundantOr = pattern`${expr} || ${expr}`;  // Matches: x || x

rewrite() - Transformation Rules

Combine patterns and templates into rewrite rules:

const swapOperands = rewrite(() => {
    return {
        before: pattern`${"left"} + ${"right"}`,
        after: template`${"right"} + ${"left"}`
    };
});
const updated = await swapOperands.tryOn(this.cursor, binary);