[RN mobile] fix className style in SVG primitive

[mzorz]

Description

As explained in #9294 (comment), commits 2d47451 and b678c6d introduced a change that makes sure to convert a string className value to a style object for ReactNative to work properly without needing to strip the className altogether (and thus losing any intended modifiers, as is currently being done in master).
These commits were removed somehow after introducing #9685 and applying the "older" #9294 after it, so this PR only brings this change back as originally intended.

How has this been tested?

To test how this works:

1. make sure to add the following sample/test code

.dashicons-editor-bold {
	transform: rotate(20deg);
}

to packages/components/src/dashicon/style.scss

2. Run the mobile Gutenberg app

This way the styles get passed to the svg component, this is how the bold icon gets rendered:

Verify the B icon is slightly (20 degrees) leaning to the right as seen in the screenshot

Types of changes

Bug fix

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[hypest]

LGTM!

I verified that the "B" is leaning 20º the the right! ;)