[Doctrine] `StoreAsFilename`

[kbond]

If using StoreAsPath and all your filename prefixes are the same (ie some/dir/filename.ext) it can be a waste of resources to store the same prefix in the db over and over.

I propose a StoreAsFilename mapping:

#[StoreAsFilename(
    filesystem: 'public'
    fileNamer: new Expression('{this.title|slug}-{name}{ext}'), // would throw an exception if contains /'s
    directoryNamer: new Expression('some/dir'),
)]
private File $file;

When saving to db, just the filename would be stored. When loading, the directoryNamer would be used to create the prefix and append the filename to it.

As a slight perf boost, we could add a String Namer that doesn't require processing and just returns the string. Probably a SelfGeneratingNamer concept should be added.

#[StoreAsFilename(
    filesystem: 'public'
    fileNamer: new Expression('{this.title|slug}-{name}{ext}'),
    directoryNamer: new String('some/dir'),
)]
private File $file;