Improvements to attachment and image classes

[gchtr]

In #2753, @nlemoine mentioned quite a few points we can improve in the file and attachment classes in a future version of Timber. I’m adding these as a separate issue so we don’t lose track of it.

Things to consider:

• Remove path() methods in all models. Same reason as n°1 mentioned above: I don't think models need this method. If you want a relative path for something (src, link, etc.): use the relative filter or use a WP filter/plugin. Plus I don't think we need a helper to get the relative URL, there's already one in WP.
• Do you know what's the abs_url for?

  timber/src/Attachment.php

  Line 65 in 99f7a1a

  public $abs_url;

  
  This feels redundant with $image->src()
• I think we should remove the maybe_secure_url helper. If the URL is http, then it's a somewhere else problem that will be hidden (and not fixed and brought to the developer attention) by this fix that's not Timber in Timber's scope IMHO.
• Same goes for remove_double_slashes: we shouldn't aim at fixing every issues whose causes are elsewhere in the stack.

and

• image dimensions are still read from file, which could be avoided by getting image metadata for registered sizes and improve performance. But would require quite some refactoring (ImageDimensions doesn't takes some $metadata to look for dimensions)

• I noticed that ImageHelper::sideload_image() is very optimistic 😅 There are some places in that method that can go wrong and are not handled:

  • the extension parsing is not covering all possible cases
  • the download_url result should be handled as soon as it is is returned
  • there is no handling of the possible error index of wp_upload_bits()