bug#71698: 29.3; comint--intersect-regions fontifies some output using input function

[JD Smith]

A bit more context, to quote from the manual:

> When the characters before and after POS are part of the same field,
> there is no doubt which field contains POS: the one those characters
> both belong to. When POS is at a boundary between fields, which field
> it belongs to depends on the stickiness of the ‘field’ properties of the
> two surrounding characters (*note Sticky Properties::).  The field whose
> property would be inherited by text inserted at POS is the field that
> contains POS.

Note that comint adds `field' as `rear-nonsticky' on the prompt, but this does 
not impact the inheritance of the field from the previous character or the 
behavior of field-beginning (only a front-sticky on the following character 
would do so).