Add javadoc on internal UUID format

[ZacBlanco]

Description

Adds a javadoc for presto-native developers to reference the internal format of UUIDs

Motivation and Context

Helps better specify the format to maintain compatibility

Impact

N/A

Test Plan

N/A

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[ZacBlanco]

Discussed with @BryanCutler about this who has been working on the Presto native support. This will be the officially-documented format for now. However, in the future we would like to update our slice library to be able to perform comparisons without byte swapping the longs internally. This should improve performance for UUIDs in both java and native. The improvement to the behavior of byte-wise comparisons in slices will likely be done in tandem with the JDK upgrade as it allows us to use some new JDK libraries to do this comparison.

[BryanCutler]

LGTM, thanks!

[steveburnett]

A couple of nits, nothing significant. Thanks for the doc.

[aditi-pandit]

Thanks @ZacBlanco

[imsayari404]

Thanks @ZacBlanco

[ScrapCodes]

Wrapping in a <pre> ... </pre> block might be better

[ScrapCodes]

Suggested change

	*
	* </pre>

[ScrapCodes]

Suggested change

	*
	* <pre>

[hantangwangd]

Thanks for the Clarification.

Steve is OOO