Use WebKit-native content filters for blocking.

[aartaka]

Description

WebKit has a mechanism of content filters to fully or partially block/modify the loaded pages. It's supposed to be lightnight-fast, especially compared to our blocker-mode that often takes some second to inspect an especially big page.

DOES NOT WORK YET, I'm trying to figure why. Not likely to be ready soon enough, because I'm occupied with other stuff and this fix that I supposed to be a quick one—turned out slightly harder than a quick one.

Checklist:

Everything in this checklist is required for each PR. Please do not approve a PR that does not have all of these items.

• Git hygiene:
  • I have pulled from master before submitting this PR
  • There are no merge conflicts.
• I've added the new dependencies as:
  • ASDF dependencies,
  • Git submodules,

    cd /path/to/nyxt/checkout
    git submodule add https://gitlab.common-lisp.net/nyxt/py-configparser _build/py-configparser

  • and Guix dependencies.
• My code follows the style guidelines for Common Lisp code. See:
  • Norvig & Pitman's Tutorial on Good Lisp Programming Style (PDF)
  • Google Common Lisp Style Guide
• I have performed a self-review of my own code.
• My code has been reviewed by at least one peer. (The peer review to approve a PR counts. The reviewer must download and test the code.)
• Documentation:
  • All my code has docstrings and :documentations written in the aforementioned style. (It's OK to skip the docstring for really trivial parts.)
  • I have updated the existing documentation to match my changes.
  • I have commented my code in hard-to-understand areas.
  • I have updated the changelog.lisp with my changes if it's anything user-facing (new features, important bug fix, compatibility breakage).
    • Changelog update should be a separate commit.
  • I have added a migration.lisp entry for all compatibility-breaking changes.
  • (If this changes something about the features showcased on Nyxt website) I have these changes described in the new/existing article at Nyxt website or will notify one of maintainters to do so.
• Compilation and tests:
  • My changes generate no new warnings.
  • I have added tests that prove my fix is effective or that my feature works. (If possible.)
  • I ran the tests locally ((asdf:test-system :nyxt) and (asdf:test-system :nyxt/gi-gtk)) and they pass.

[jmercouris]

Please reopen when ready.