feat: add Screenshot plugin

[robingenz]

Name

Screenshot

Platform(s)

• Android
• iOS
• Web

Description

One of my customers is looking for a Capacitor plugin that allows him to take a screenshot of the WebView (html -> image) in case of errors in the app. This plugin should be available on Android, iOS and on the Web. On the Web, html2canvas can be used and the image should be returned as Data URL. On Android and iOS, the image should be saved on the local filesystem in the cache directory with a unique filename (e.g. uuid).

I think of the following types:

export interface ScreenshotPlugin {
  /**
   * Take a screenshot.
   * 
   * @since 6.0.0
   */
  take(): Promise<TakeResult>;
}

/**
 * @since 6.0.0
 */
export interface TakeResult {
  /**
   * The file path (Android and iOS) or data URI (Web) of the screenshot.
   * 
   * Only available on Android, iOS and Web.
   * 
   * @since 6.0.0
   * @example 'content://com.android.providers.downloads.documents/document/msf%3A1000000073'
   * @example 'data:image/jpeg;base64,SGVsbG8sIFdvc...mxkIQ=='
   */
  uri: string;
}

Additional context

No response

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[robingenz]

@ebarooni Feel free to work on this issue. I've pushed the boilerplate code to feat/issue-343. Please create your own branch based on my branch to be able to create a PR against feat/issue-343. This way we can review just the implementation changes.