[Leo] Support modifying user prompt on iOS

[yrliou]

Platforms

iOS

Description

brave/brave-core#24558 only makes it compile on iOS with new API changes, this issue is for tracking the iOS work to support it.
cc @StephenHeaps

[hffvld]

Verified on iPhone 14 and iPad Mini (6th gen) using version(s):

Device/OS: 
- iPhone 14 / iOS 17.7
- iPad Mni (6th gen) / iPadOS 18
Brave build: 1.70 (123)
BraveCore: 1.70.123 (129.0.6668.89)

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STEPS:

1. Launch Brave
2. Open Leo
3. Type any query > Send request
4. Wait for Leo's response
5. Tap and hold your query > Verify, that Edit Promt exist
6. Tap Edit Prompt > Edit your query > Tap ✅ > Verify that the Edited button appeared, and the timestamp is updated

ACTUAL RESULTS:

• Verified that the user can edit a query.
• Verified that Leo gives a new response to an updated query.
• Verified that the Edited label appeared on the right side.
• Verified that the string contains Edited with a new timestamp updated each time after the query was updated.

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iPhone 14 / iOS 17.7

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2024-10-01_17-42-41.mp4

iPad Mni (6th gen) / iPadOS 18

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