RFR: 8251495: Clarify DOM documentation

[Joe Wang]

On Wed, 9 Sep 2020 23:15:58 GMT, Lance Andersen <lancea at openjdk.org> wrote:

>> Revert changes made by JDK-8249643, removing the implNote.
>
> Based on the spec review and follow-on discussions, this change makes sense

An implNote was added to the DOM's package description in an attempt to document the JDK implementation's deviation
from the DOM specification. However, a further study showed that was incorrect because the XML specification did
include range [#x10000-#x10FFFF]. The Impl's interpretation was based on the clause "excluding the surrogate blocks".
The problem was it used Java char to determine it. Thus instead of excluding the surrogate blocks with codepoints
ranging from U+D800 to U+DBFF and U+DC00 to U+DFFF, it converted characters with a Java representation of a surrogate
pair into character references.

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PR: https://git.openjdk.java.net/jdk/pull/100