fix(jp): translate remaining English paragraphs in data-grid Feature block

[IG-Mori]

Summary

• Translated two untranslated English body paragraphs inside the <Feature> block of docs/xplat/src/content/jp/components/grids/data-grid.mdx
• The paragraphs had been carried over in English from a previous version and were not addressed in the original SEO update PR

Changes

• Paragraph 1 (L26): Translated the Data Grid component description paragraph (preserved <PlatformBlock> markup)
• Paragraph 3 (L28): Translated the performance/speed description paragraph

Reviewer Notes

• The untranslated second paragraph (L27) was not touched as it was not part of the diff in the source PR
• All other changes (title, H1 heading) from the source PR are left as-is

[IG-Mori]

@ChronosSF
I have created a PR for #369.
My understanding is that #369 contains text that has not been translated into Japanese. This PR translates that text.
If there are no issues with translating it into Japanese, please merge this PR.
If you prefer to keep it in English, please reject this PR.

If it is correct that this is translated into Japanese, may I go ahead and merge it at my own discretion if I find the same thing in the future?