doc: improve 'hex' Buffer decoding description and examples

[gioragutt]

Fixes: #41594

[benjamingr]

Please run the linter 🙏 ( the word 'hexadecimal' needs to drop a line)

[tniessen]

Unfortunately, it doesn't matter much if the strings exclusively contain hexadecimal characters. In fact, it might be more surprising that Buffer.from truncates data even when it only contains hex digits:

// only hex, still truncated :(
Buffer.from('000', 'hex').toString('hex') === '00'

[gioragutt]

Is it because it reads 2 characters at a time?

[gioragutt]

Nvm, read the docs, which state:

Buffer.from('1a7g', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').

So the last '0' is truncated because it's a single character, and the hex decoder expects pairs of characters.
So since the third '0' does not have a pairing character, it is truncated.

Perhaps the description should state that? You know, not only in the code example?

[tniessen]

Suggested change

	may occur when decoding strings that do not exclusively contain valid
	hexadecimal characters. See below for an example.
	may occur when decoding strings that do not exclusively consist of an even
	number of hexadecimal characters. See below for an example.

Maybe something like this?

[gioragutt]

I think that this, plus another code example (something like 123 -> 12) would be very nice

[gioragutt]

@tniessen WDYT?

[tniessen]

SGTM. These are unfortunate oddities that we need to maintain for backward compatibility :(

[gioragutt]

I took a better look at the examples and figured that I could achieve the same thing by altering the strings used in the examples.

[Trott]

Optional nit-pick suggestion: The Microsoft style guide we follow suggests might instead of may in this context. But I wonder if it's actually will occur rather than might occur? All told:

Suggested change

	* `'hex'`: Encode each byte as two hexadecimal characters. Data truncation
	may occur when decoding strings that do exclusively contain valid hexadecimal
	characters. See below for an example.
	may occur when decoding strings that do not exclusively consist of an even
	number of hexadecimal characters. See below for an example.
	* `'hex'`: Encode each byte as two hexadecimal characters. Data is truncated
	when decoding strings that do not exclusively consist of an even
	number of hexadecimal characters. See below for an example.

[aduh95]

Landed in dbe60a2