refactor(tauri): inject script with webview init API

[lucasfernog]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• New Binding Issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes. Issue #___
• No

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

Changes the loading mechanism of the Tauri JS script (entry point). Previously was just a <script> tag on index.tauri.html, which had problems when the app changes the HTML page in an old school way (who needs SPAs?). Now we add a __tauri.js file on the same folder as index.tauri.html and read it on the app build script.