[Files] Design feedback for the upload component

[jloleysens]

@mdefazio 's feedback:

Uploading a file

Should the text inside the file upload simply say 'Select or drop a file' to be more concise? Removes the extra conjunction.

When uploading the file, let's use the loading button , and then change it to a success button with the check icon. The label could then say 'Upload complete'. We would not need to use the pink line loading indicator in this case then. I would imagine this would be the same behavior for the Basic and Allow repeated uploads options.
The Long error scenario should also use the default button, instead of an empty button. Though in this case, we could use the danger styling. The error messages seem fine though.

If I abort the upload, should that message not appear somewhere? Also switching this to a default button rather than empty like the other scenarios can help keep this upload button the main focus. Perhaps reusing the Max size option here, but simply changing the text to 'File upload cancelled'

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesUx)

[jloleysens]

Original comment: #143111 (review)

[jloleysens]

Should the text inside the file upload simply say 'Select or drop a file' to be more concise? Removes the extra conjunction.

This is the default text in the EUI upload component. For this component we do allow users to override this default per their use case 😊