test: add comprehensive tests for GetHorizontalFrameSize, GetVerticalFrameSize, GetFrameSize

[XelHaku]

Summary

Adds dedicated tests for GetHorizontalFrameSize, GetVerticalFrameSize, and GetFrameSize with comprehensive coverage across border types, padding, margins, and their combinations.

Motivation

The underlying bug in GetHorizontalFrameSize was fixed in #411, but the tests added there were lost during a revert (see #353). This adds them back with expanded coverage.

Test coverage

• Default (zero) state — no style set returns 0
• Padding only — asymmetric padding values
• Margins only — asymmetric margin values
• Border types — Normal, Rounded, Double, Thick, Hidden
• Combinations — border + padding, border + padding + margins
• Partial borders — single-sided borders, all sides unset
• GetFrameSize — verifies both return values simultaneously

All 23 test cases verify the frame size breakdown: frame = border + padding + margins.
No existing tests were modified.