[Bug]: USD denomination of conversion

**Describe the bug**

As a user that wants to convert USDC to mUSD, it is more natural for me to enter the USDC amount I want to convert, not its USD-equivalent

**Screenshots/Recordings**

**Steps to reproduce**

1. Open MetaMask mobile app
2. Navigate to a supported network with USDC available
3. Ensure you have USDC in your wallet
4. Click on "Convert to mUSD"
5. Observe the input field on the conversion screen
6. Note that the input is for USD-equivalent amount (e.g., $100)
7. Attempt to enter the USDC token amount you want to convert (e.g., 50 USDC)

**Error messages or log output**

```shell

```

**Where was this bug found?**

Internal release testing

**Version**

7.62.123

**Build number**

3445

**Build type**

None

**Device**

Moto G Power

**Operating system**

Android