WIP: Fix browser specific imports for the rust-bindings library.

[soerenbf]

Ref COR-2050

Purpose

Concordium/concordium-browser-wallet#658 can currently not use version 12.0.0 due to the following entrypoints not working:

  "exports": {
    ".": {
      "browser": {
        "module": "./lib/dapp/web/umd/index.min.js",
        "types": "./lib/dapp/web/esm/index.d.ts",
        "import": "./lib/dapp/web/esm/index.js",
        "default": "./lib/dapp/web/umd/index.min.js"
      },
    },
    "./dapp": {
      "browser": {
        "module": "./lib/dapp/web/umd/index.min.js",
        "types": "./lib/dapp/web/esm/index.d.ts",
        "import": "./lib/dapp/web/esm/index.js",
        "default": "./lib/dapp/web/umd/index.min.js"
      },
    },
    "./wallet": {
      "browser": {
        "module": "./lib/wallet/web/umd/index.min.js",
        "types": "./lib/wallet/web/esm/index.d.ts",
        "import": "./lib/wallet/web/esm/index.js",
        "default": "./lib/wallet/web/umd/index.min.js"
      },
    },
  },

Ideally when testing this, we should verify that the build works when used within https://github.com/Concordium/concordium-browser-wallet/

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[soerenbf]

Verified that this works in the context of the browser wallet.