ja: use the Japanese geometry terms

[yasumorishima]

Fifth of the small PRs from #715, independent of #720, #721, #722 and #723.

What is wrong

The seeded geometry rules and the geometry entries of definitions.yaml transliterate the English words rather than use the Japanese terms. For this area the terms are completely settled -- they are what a textbook introduces in the first year of junior high.

	seeded	term
line segment	ラインセグメント	線分
directed line segment	ラインセグメント	有向線分
line	ライン	直線
ray	レイ	半直線
arc	アーク	弧
point	ポイント	点
area	エリア	面積
angle	アングル	角
angle measure	角度測定 / 角度の測定	角の大きさ

Two of these are more than word choice:

• line-segment and directed-line-segment were both ラインセグメント, so the distinction between them disappeared.
• 角度測定 reads as "measuring an angle measure" -- 角度 already is the measure of an angle. The quantity is 角の大きさ.

The Verbose branches were English word order carried over with the wrong particles (「ラインセグメントから A に B」); they now read 「線分 A から B まで」.

A ray does not stop at its second point

en says "the ray from A to B", where "to" means "in the direction of". Rendering that with 「まで」 claims the ray ends at B. A ray has A as its endpoint and continues through B without end, so Verbose reads 「半直線 A を始点として B を通る」. A segment does end at its second point, so から...まで is right there. The second commit fixes this and adds a test that pins the two apart; CodeRabbit caught it on my preflight branch.

Deliberately not touched

• The word order. 「AからBまでの線分」 is more idiomatic prose, but the reference this series follows opens by saying to keep to the English reading order and not presuppose reversal, and postposing the head term is the kind of structural divergence from en I asked about in ja: read fractions in Japanese word order #720 and Create a Japanese (ja) translation #715.
• アークタンジェント and the other inverse trig names, which are correct as they stand -- only the geometric アーク is a transliteration.

山口雄仁・川根深・澤崎陽彦「日本語による数式読み上げ法の基本構成について」日本数学教育学会誌 78(9), 239-247 (1996)

Tests

geometry_terms (the five intent forms), geometry_point, and geometry_verbose_from_to (segment against ray under Verbose).

Spotted, left for later

In the same block of definitions.yaml, change (Δ) is 変更点, "a point that was changed"; the quantity is 変化量.