Add symbols for ST KFxxBDT Linear Regulators

Add symbols for ST KFxxBDT Linear Regulators

As the title says.

Adding symbols for the TO-252 package options from https://www.st.com/resource/en/datasheet/kfxx.pdf.

All symbols are derived.

All contributions to the kicad library must follow the KiCad library convention

Thanks for creating a pull request to contribute to the KiCad libraries! To speed up integration of your PR, please check the following items:

• Provide a URL to a datasheet for the symbol(s) you are contributing
• An example screenshot image is very helpful
• Ensure that the associated footprints match the official footprint library
  • A new fitting footprint must be submitted if the library does not yet contain one.
• If there are matching footprint PRs, provide link(s) as appropriate
• Check the output of the automated check scripts - fix any errors as required
• Give a reason behind any intentional library convention rule violation.