OID first two components encoded/decoded incorrectly

[nealian]

I noticed what I believe to be an error in the ObjectIdentifier code for the first two components.

In the python-asn1 code, it seems like there is a (completely understandable) assumption that the first two OID components should each be <= 39.
It seems like the synopsis version on OSS's BER page is somewhat confusing.
However, going through to the actual specification, the rules are actually laid out somewhat clearer.

The specification for BER/DER are in ITU-T X.690, and specifically for OIDs in (02/2021) section 8.19.

The trick for the first "subidentifier" (series of octets encoding a single number) is that the separate (non-joint) roots for ITU-T and ISO (0.y and 1.y, respectively) only have immediate children with numerical value less than 40. However, this is not true for the joint root, 2.y.

The text of section 8.19.4 should then be read under this new light.

The numerical value of the first subidentifier is derived from the values of the first two object identifier components in the object identifier value being encoded, using the formula

$$ (X*40) + Y $$

where $X$ is the value of the first object identifier component and $Y$ is the value of the second object identifier component.

NOTE - This packing of the first two object identifier components recognizes that only three values are allocated from the root node, and at most 39 subsequent values from nodes reached by $X = 0$ and $X = 1$.

My reading of this is that $X \le 2$, and, for $X = 2$, $Y$ can be arbitrarily large.

Indeed, they have an example in the following section (8.19.5), such that the example OID 2.999.3 (hey, it turns out that 2.999 is the OID you're supposed to be using for generic OID examples anyway!) is encoded into the decimal subidentifiers (1079, 3) and therefore bytes

b'\x06\x03\x88\x37\x03'

(This should address #279 as well, though the scope of this issue is a little larger.)

I am working on a PR to apply the necessary (and breaking) changes to the encoder, decoder, and tests.