Add modern exports

[kibertoad]

This PR (delete as applicable)

• Adds a new feature

Describe the changes below:

In order to use headless version of Phaser with vitest, an explicit alias is needed in the configuration:

    resolve: {
        alias: {
            // Phaser's "main" points to source that requires the devDependency
            // phaser3spectorjs. Redirect to the pre-built ESM bundle instead.
            phaser: "phaser/dist/phaser.esm.js",
        },
    },

This is unnecessary and ideally should be handled by explicitly defined export, which are added in this PR. I have validated that after this change alias is no longer necessary, vitest just works.