fix: radio button reactive form

[rengare]

Please provide a link to the associated issue.

Relates #2304

Please provide a brief summary of this pull request.

PR brings fix for radio button inside reactive forms

Please check whether the PR fulfills the following requirements

• the commit message follows the guideline:
  https://github.com/SAP/fundamental-ngx/blob/master/CONTRIBUTING.md
• tests for the changes that have been done

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[droshev]

errors during build:

8:23:01 PM: ERROR: libs/core/src/lib/radio/radio-button/radio-button.component.html(7,5): Property 'actualValue' does not exist on type 'RadioButtonComponent'.
8:23:01 PM: An unhandled exception occurred: libs/core/src/lib/radio/radio-button/radio-button.component.html(7,5): Property 'actualValue' does not exist on type 'RadioButtonComponent'.

[InnaAtanasova]

1. The radio-button template calls actualValue and gives build errors.
2. In the component file you have writeValue which is defined but never used

[rengare]

1. The radio-button template calls `actualValue` and gives build errors.

2. In the component file you have `writeValue` which is defined but never used

2. writeValue comes from ControlValueAccessor interface implementation, its mandatory

[rengare]

errors during build:

8:23:01 PM: ERROR: libs/core/src/lib/radio/radio-button/radio-button.component.html(7,5): Property 'actualValue' does not exist on type 'RadioButtonComponent'.
8:23:01 PM: An unhandled exception occurred: libs/core/src/lib/radio/radio-button/radio-button.component.html(7,5): Property 'actualValue' does not exist on type 'RadioButtonComponent'.

fixed