[compiler] Add snap subcommand to minimize a test input

[josephsavona]

Snap now supports subcommands 'test' (default) and 'minimize`. The minimize subcommand attempts to minimize a single failing input fixture by incrementally simplifying the ast so long as the same error occurs. I spot-checked it and it seemed to work pretty well. This is intended for use in a new subagent designed for investigating bugs — fixture simplification is an important part of the process and we can automate this rather than light tokens on fire.

Example Input:

function Component(props) {
  const x = [];
  let result;
  for (let i = 0; i < 10; i++) {
    if (cond) {
      try {
        result = {key: bar([props.cond && props.foo])};
      } catch (e) {
        console.log(e);
      }
    }
  }
  x.push(result);
  return <Stringify x={x} />;
}

Command output:

$ yarn snap minimize --path .../input.js
Minimizing: .../input.js

Minimizing................

--- Minimized Code ---
function Component(props) {
  try {
    props && props;
  } catch (e) {}
}

Reduced from 16 lines to 5 lines

This demonstrates things like:

• Removing one statement at at time
• Replacing if/else with the test, consequent, or alternate. Similar for other control-flow statements including try/catch
• Removing individual array/object expression properties
• Replacing single-value array/object with the value
• Replacing control-flow expression (logical, consequent) w the test or left/right values
• Removing call arguments
• Replacing calls with a single argument with the argument
• Replacing calls with multiple arguments with an array of the arguments
• Replacing optional member/call with non-optional versions
• Replacing member expression with the object. If computed, also try replacing w the key
• And a bunch more strategies, see the code