gh-143990: Preserve the size when creating a Font from a named font (GH-153267)

gh-143990: Preserve the size when creating a Font from a named font (GH-153267)

tkinter.font.Font now copies the options of a named font (via "font
configure") instead of the options resolved by "font actual", which
would resolve a size specified in pixels (a negative size) to points.
A font description is still resolved, as it cannot be parsed otherwise.

Font.copy(), which has always been equivalent to constructing a Font
from the original font, is updated to match and now preserves the size
too.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>