patch 9.1.2129: MS-Windows: font size calculation slightly wrong, causing line gaps

patch 9.1.2129: MS-Windows: font size calculation slightly wrong, causing line gaps

Problem:  MS-Windows: font size calculation slightly wrong, causing
          vertical line gaps (Maxim Kim, after v9.1.2127)
Solution: Update font size calculation when using DirectX
          (Yasuhiro Matsumoto).

Use pre-calculated font ascent from font metrics instead of fixed
formula (h * 0.83) to calculate text baseline. This prevents vertical
text shift when font fallback occurs with CJK characters.

closes: #19318

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>