fix: use content hash as [base] and [name] for extracted DataURI's

[alexander-akait]

What kind of change does this PR introduce?

bugfix, prevent name conflicts for extracted DataURI's

Did you add tests for your changes?

Yes

Does this PR introduce a breaking change?

No

What needs to be documented once your changes are merged?

No

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)