Fix +91 Prefix in Mobile Number Field

[aravindm4]

Description:
Currently, in the mobile number field, the “+91” prefix is editable or removable. Need to make the “+91” prefix fixed and non-deletable, ensuring that users cannot modify or remove it.

[AdityaJ2305]

Hey @aravindm4 , I am assuming you are talking about the forms where we only support indian numbers to be filled as of now and that too the Phone number field is getting updated in this issue #9966

Cc: @rithviknishad

[rajku-dev]

What if user need to change country code?
Do we need to keep the country code non-editable.

[rithviknishad]

Completed in #10214