How to access link fields (url and text) value separately in views template?
The Easy way in Views UI add field_link 2 times.

in 1) Exclude from display, Select url only, and Show url as plain text.
which will give you the url only.



in 2) Exclude from display, and REWRITE RESULTS -> Strip HTML tags
which will give you the  title only.



Then in a custom field you can use twig  URL: {{ field_link }} Url Title: {{ field_link_1 }}

then in your custom template you can use them ... 

Option 2) almost as easy create a custom field formatter based on 
Drupal\link\Plugin\Field\FieldFormatter\LinkSeparateFormatter.php