Replicate Babel's `optimizeConstEnums` transformation

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`](https://babeljs.io/docs/babel-preset-typescript#optimizeconstenums) does the following:

```ts
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.

The issue names no source files or tests. Start by locating esbuild's TypeScript const-enum lowering and compare its output with Babel's optimizeConstEnums examples. Done means const enums produce plain objects, including the demonstrated handling of duplicate declarations.

Written by the indexing model from the issue text.