API allow chaining for Upload_Validator

[wilr]

No description provided.

[emteknetnz]

Seems fine, matches what happens often happens elsewhere with set methods e.g.

• https://github.com/silverstripe/silverstripe-framework/blob/4/src/Forms/Validator.php#L150
• https://github.com/silverstripe/silverstripe-framework/blob/4/src/Forms/GridField/GridFieldExportButton.php#L283

Could you add a simple unit test that chains everything together and asserts that $this is returned.

[wilr]

Could you add a simple unit test that chains everything together and asserts that $this is returned.

Test added

[emteknetnz]

@maxime-rainville you OK with changing the pseudo API signature of what's functionally changing the return type of :void to :Upload_Validator?

I think this is fine for a minor since nothing will be relying on a return value right now, and I don't think think there's really anything else we'd return. Possible exception may be clearErrors() since it's not a set function, though I can't really imagine why we'd every return a bool or array for this method

[GuySartorelli]

Retargetted to 2 and rebased. If CI passes fine I'll be happy to merge this - it's not BC breaking by our current standards.