Load picture srcset from partial

[marcorieser]

Sometimes the default picture srcset definition is not ideal for a specific case or the whole project. At the moment the only solution would be to alter the picture partial by publishing it but this cuts it off from future updates in the addon.

I was wondering if it wouldn't be nice to override the default definition by publishing just the default definition, or to pass a different definition for a specific case.

Due to when / how Antlers evaluates the variables the definition has to be in a partial.

{{# Uses the default definition (no changes) #}}
{{ partial:statamic-peak-tools::components/picture ... }}

{{# Uses a custom definition by passing a path #}}
{{ partial:statamic-peak-tools::components/picture ...  srcset_from="path/to/definition" }}

{{# the definition in `path/to/definition` #}}
{{ srcset = [
   ... 
  [ 'width' => 3840, 'ratio' => '{ ratio_large ?? ratio ?? original_ratio }' ],
] }}

Changes proposed in this pull request:

• Extract the default srcset definition to a dedicated partial
• Adds the ability to pass a path to a partial which holds an alternative definition for the srcset variable

[marcorieser]

Appropriate location for the default definition has to be defined.

[robdekort]

Nice work. The snippets folder seems fine to me.

[robdekort]

And perhaps this is a nice chance to rename srcsets to srcset (not plural).

[marcorieser]

Since the Maestro Koster has no better approach for overwriting the variable, I'd release it in to the wild.