Replicate Babel's optimizeConstEnums transformation

[mary-ext]

Unlike regular enums, const-based enums do not have reverse mapping, and can't be referenced and indexed the same way.

Given that we're already ignoring isolatedModules behavior of not inlining const-based enums at all even within the same file, why not go a step further and transform const enum into a plain object literal? Babel's optimizeConstEnums does the following:

export const enum LabelPreference {
  Ignore = 1,
  Warn = 2,
  Hide = 3,
};

// transformed to...

export var LabelPreference = {
  Ignore: 1,
  Warn: 2,
  Hide: 3,
};

// duplicate enum declarations gets transformed to:
Object.assign(LabelPreference, {
  Blur: 3,
});

The size reduction from this transformation seems worthwhile for libraries trying to bundle with esbuild.