RFR: JDK-8276800 Fix table headers in NumericShaper.html

[Ludvig Janiuk]

On Mon, 8 Nov 2021 09:13:35 GMT, Ludvig Janiuk <duke at openjdk.java.net> wrote:

> This change introduces no visual difference, but improves a11y.

I've pushed a change which "ticks the boxes without introducing so much change". I keep the first column as the row header, and simply specify it explicitly on the `td` elements. Doccheck is fine with it.

@aivanov-jdk If you thinks this works, I'd ask you to review and sponsor (if the review is necessary given the existing, outdated one).

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PR: https://git.openjdk.java.net/jdk/pull/6291