[file_selector_android] Refactor interactions with ContentProvider provided filenames

[gmackall]

https://developer.android.com/privacy-and-security/risks/untrustworthy-contentprovider-provided-filename#don%27t-trust-user-input

Adapted from this option
https://developer.android.com/privacy-and-security/risks/untrustworthy-contentprovider-provided-filename#sanitize-provided-filenames

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