feat: add eval support for link field filters

[RitvikSardana]

Users can add dynamic filters based on some value from the form.

Use:

eval: doc.fieldname

or

eval: doc.fieldname1 + doc.fieldname2

Screen.Recording.2024-03-14.at.11.16.54.PM.mov

For Child Tables
2 types of filters can be added.

• From the Child Table Row: to add these filters use doc.child_table_field_name

• From Parent Document: to add these use parent.parent_doc_fieldname

Screen.Recording.2024-03-19.at.12.21.08.PM.mov

the expression added after "eval:" is evaluated and its value is returned.

docs: https://docs.erpnext.com/docs/user/manual/en/creating-custom-link-field#adding-filters-to-link-field

[ankush]

Mark as ready when done

[barredterra]

If they are part of the doctype definition already, can we also validate these filters in the backend? A common cause of unexpected behavior is when filters are set but users can still circumvent them, for example by pasting a different value or using the browser console.

[ankush]

@barredterra eval stuff will be JS so again it will hard to redo it in server side.

Also, we are starting a client rewrite project soon-ish, we'll figure out a better way to represent some of these things so they can be validated on both client and server side. (Not just search field but other validations too)

[ankush]

@GursheenK @ruchamahabal FYI ^