Added pointer cursor on theme, plugin, and media uploader

[Ankit K Gupta]

If theme and plugin button will have pointer on hover, it will increase the user accessibility.
Other uploader have pointer as well.
As uploader have wide area for selecting the file.. Would be great if have pointer.

[Ankit K Gupta]

35552- Patch file

[Ankit K Gupta]

Screenshot of uploader

[afercia]

Probably, the reason why these file upload inputs are not styled is because, historically, they have always been very difficult if not impossible to style due to the fact this kind of inputs depends on the operating system, especially the "browse" button. Modern browsers allow some more styling through the shadow-DOM and exotic proprietary CSS selectors but honestly I think it's better to stay away from that and do just what is proposed in this ticket :)
Using the pointer cursor is a nice, small, improvement and I don't see any reason why it shouldn't be done. +1 from me.

[afercia]

Refreshed patch resets the cursor style to default if the input field is, by chance, disabled.

[afercia]

In 38435:

Accessibility: Improve the file upload inputs styling.

Though browsers implement cursor: pointer on this kind of controls a bit
inconsistently, the pointer cursor styling makes more clear the button and
label are actionable controls.

Props Ankit K Gupta.
Fixes #35552.