Fix: Enable sharing .txt files for import in AnkiDroid

[SanjaySargam]

Purpose / Description

This PR adds the necessary intent-filter configuration to the AndroidManifest.xml to enable AnkiDroid to handle .txt files shared from the file manager for import

Fixes

• Fixes Missing Share Option for .txt Files while Importing #17873

Approach

Added intent-filter for text/plain MIME type to support .txt file sharing and import

How Has This Been Tested?

Physical Device (Redmi Note 13)

WhatsApp.Video.2025-01-26.at.4.02.43.PM.mp4

Learning (optional, can help others)

Describe the research stage

Links to blog posts, patterns, libraries or addons used to solve this problem

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[david-allison]

• Related: refactor: de-duplicate .csv/.tsv values both in IntentHandler and in ImportFileSelectionFragment #17875

[david-allison]

Cheers!

[lukstbit]

LGTM, thanks!