`interaction.TextLineField` has broken `default=` semantics in CLI

Version and Platform (required):

• Binary Ninja Version: 5.0.7280-test Ultimate (9ef1367f)
• OS: Debian
• OS Version: trixie
• CPU Architecture: x64

Bug Description:
In the GUI, the default value is pre-filled in the field, which works out.

In the CLI, it is never used no matter how the API is called.

Steps To Reproduce:

>>> import binaryninja
>>> binaryninja.get_form_input([f := binaryninja.TextLineField("Type:", default="AAA")], ""); f.result
Type: 123
'123'
>>> binaryninja.get_form_input([f := binaryninja.TextLineField("Type:", default="AAA")], ""); f.result
Type: 
''

Expected Behavior:
One of:

1. Default value is pre-filled and can be erased by pressing Backspace.
2. Default value is returned when no input is entered. (While this makes entering an empty string impossible, it's easier to work around that than around lack of default values.)

Start by reproducing the behavior with binaryninja.TextLineField and binaryninja.get_form_input in the CLI, using the examples in the issue. Trace the CLI handling of the default value and compare it with the GUI behavior. Done means the documented default semantics work consistently and the reported empty-input cases are covered by tests.