Mobile: Resolves #11846: Improve encryption config screen accessibility

[personalizedrefrigerator]

Summary

This pull request's goal is to improve the accessibility of the encryption config screen. In particular, it:

• Labels headers as headers, labels a link as a link (WCAG 2.2 SC 4.1.2 "Name, Role, Value", WCAG 2.2 SC 1.3.1 "Info and relationships")).
• Better describes the emoji used to mark a password as valid or invalid.
• Adds labels to the "Password:", "Confirm password:", and "Enter the master password" inputs (Android and web only) (WCAG 2.2 SC 4.1.2 "Name, Role, Value", WCAG 2.2 SC 1.3.1 "Info and relationships")).
• Hides the "disabled keys" dropdown when there are no disabled keys.
  • The "Disabled" dropdown could potentially be confusing when empty.

Remaining work

There are a few issues not addressed by this pull request:

• The documentation link should be better described.
• There's no status announcement when clicking "Save" for a secondary key, if the password remains invalid.
• Inputs for secondary passwords do not have a programmatically-associated label.

Testing

This pull request adds automated tests that verify:

• The "disabled keys" dropdown is only shown when there are disabled keys.
• The "master password is not set" input is shown when there is no master password (and encryption is enabled).

Limited manual testing has also been done on web:

• Verified that the documentation link is described as a link.
• Verified that the "status" and "master key ..." headings are marked as headings.
• Verified that the "password" and "confirm password" inputs (shown when first setting up encryption) have labels.
• Verified that the "X" emoji is described as "Invalid password, image".