Check to avoid harcoding methods in field definition

[luisg123v]

Cases like:

name = fields.Char(
    compute=_compute_name,
    default=_default_name,
)

Should be avoided because:

• Methods are harcoded, which means they can't be inherited, because set methods are from that specific class, instead of model methods.
• We are forced to define such methods above field definition, which is against our guidelines, which specifies fields should go first, then methods.

Instead, the following should be done:

name = fields.Char(
    compute="_compute_name",
    default=lambda self: self._default_name(),
)

i.e. passing computed method as a string and default method as a lambda.

Attributes to consider for both cases

The following attributes support receiving a string:

• compute
• inverse
• search
• selection

(See the odoo.fields.determine method for more info and all the places where it is called)

The following attributes do not support receiving a string, hence they require passing a lambda:

• default
• domain
• translate
• ondelete (dictionary values, not the dictionary itself)

(See all appearances of the callable() function in odoo.fields)

Discouraging cases like the above will prevent issues like odoo/odoo#185419.

CC @moylop260 @teposteaj