encoding/asn1: only accept minimally encoded base 128 integers

Reject base 128 encoded integers that aren't using minimal encoding,
specifically if the leading octet of an encoded integer is 0x80. This
only affects parsing of tags and OIDs, both of which expect this
encoding (see X.690 8.1.2.4.2 and 8.19.2).

Fixes #36881

Change-Id: I969cf48ac1fba7e56bac334672806a0784d3e123
GitHub-Last-Rev: fefc03d2022e10b318e532ef5a461bb46016cf12
GitHub-Pull-Request: golang/go#38281
Reviewed-on: https://go-review.googlesource.com/c/go/+/227320


Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>