RFR: 8356644: Update encoding declaration to UTF-8

[Daniel Fuchs]

On Fri, 9 May 2025 14:14:57 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> A handful of html and xml files in the JDK source tree claims to have encodings like `ISO-8859-1`, when they are in fact pure US-ASCII files.
> 
> While perhaps technically correct, this is misleading, and goes contrary to the efforts of turning the source code into UTF-8 proper.
> 
> I chose between marking them as "ASCII" and "UTF-8", but chose the latter, since otherwise if they ever were to be updated with a non-ASCII character, the value would have been unspecified, and after JDK-8301971, all files in the JDK repository will be interpreted as UTF-8.

Changes to net-properties.html LGTM

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PR Review: https://git.openjdk.org/jdk/pull/25148#pullrequestreview-2828873053