feat(ios): add per-language autocorrect toggle 🚂

[jahorton]

Build-bot: skip build:ios

User Testing

TEST_IOS_NOPREDICT: Validate "no predictions" mode for a language that supports predictive text.

1. Download this PR's version of Keyman for iPad and iOS.
2. Use the sil_euro_latin keyboard for English.
3. Using the Settings menu, drill down to Installed Languages > English.
4. Disable the top toggle - "Enable predictions".
5. Verify that the other two toggles are disabled.
6. Return to the text-editing mode.
7. Verify that a plain "image" banner with the Keyman logo appears.
8. Type tew.
9. Verify that the plain "image" banner remains.

TEST_IOS_NOCORRECT: Validate "predictions-only" mode for a language that supports predictive text.

1. Download this PR's version of Keyman for iPad and iOS.
2. Use the sil_euro_latin keyboard for English.
3. Using the Settings menu, drill down to Installed Languages > English.
4. Enable the top toggle and disable the middle toggle - "Enable corrections".
5. Verify that the last toggle is disabled.
6. Return to the text-editing mode.
7. Verify that a predictive-text banner appears.
8. Type te.
9. Verify that valid suggestions appear.
10. Type a w (resulting in tew).
11. Verify that no suggestions appear.

TEST_IOS_CORRECT: Validate "corrections, but no autocorrections" mode for a language that supports predictive text.

1. Download this PR's version of Keyman for iPad and iOS.
2. Use the sil_euro_latin keyboard for English.
3. Using the Settings menu, drill down to Installed Languages > English.
4. Enable the top two toggles and disable the last toggle - "Enable autocorrections".
5. Return to the text-editing mode.
6. Verify that a predictive-text banner appears.
7. Type tewt. (Try to use the top part of the w.)
8. Verify that valid suggestions appear.
9. Type a i (resulting in tewti).
10. Verify that no suggestion is autoselected.

TEST_IOS_AUTOCORRECT: Validate "autocorrections" mode for a language that supports predictive text.

1. Download this PR's version of Keyman for iPad and iOS.
2. Use the sil_euro_latin keyboard for English.
3. Using the Settings menu, drill down to Installed Languages > English.
4. Enable all toggles, including the last toggle - "Enable autocorrections".
5. Return to the text-editing mode.
6. Verify that a predictive-text banner appears.
7. Type tewt. (Try to use the top part of the w.)
8. Verify that valid suggestions appear.
9. Type a i (resulting in tewti).
10. Verify that the suggestion for testing is autoselected.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ⬜ TEST_IOS_NOPREDICT (OPEN)
• ⬜ TEST_IOS_NOCORRECT (OPEN)
• ⬜ TEST_IOS_CORRECT (OPEN)
• ⬜ TEST_IOS_AUTOCORRECT (OPEN)

Results Template

# Test Results

* **TEST_IOS_NOPREDICT (OPEN):** notes
* **TEST_IOS_NOCORRECT (OPEN):** notes
* **TEST_IOS_CORRECT (OPEN):** notes
* **TEST_IOS_AUTOCORRECT (OPEN):** notes