Web: Only enable default prefetching for links with 'as'

[arnorhs]

Description

Only enabling default prefetching of JS bundles, when the target bundle is known (when the 'as' prop is set on the Link component)

Note: This (along with most Link references) will have to updated anyways after next >= 9.5.3

What

Changes the NextLink generic component in the ui-core (which is probably not the right place for the component in the first place)

Why

The console spits out a bunch of 404 not founds for links defined using , but without specifying an 'as' prop (to know what kind of component it is supposed to link to)

Screenshots / Gifs

N/A

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Formatting passes locally with my changes
• I have rebased against master before asking for a review