RFR: 8320400: Make fields final in 'jdk.internal.util.xml.impl' package

[Per Minborg]

On Tue, 12 Sep 2023 19:59:57 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> A few classes in `jdk.internal.util.xml.impl` package have non-final fields which could easily be marked `final`.
> 
> Also fixed a few typos and incorrect javadoc links.

There are also some typo fixes. I think this could be mentioned in the PR description.

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PR Comment: https://git.openjdk.org/jdk/pull/15691#issuecomment-1819090804