encoding/json: fix Decoder.InputOffset regression in goexperiment.jsonv2
The Decoder.InputOffset method was always ambiguous about the exact
offset returned since anything between the end of the previous token
to the start of the next token could be a valid result.
Empirically, it seems that the behavior was to report
the end of the previous token unless Decoder.More is called,
in which case it reports the start of the next token.
This is an odd semantic since a relatively side-effect free method
like More is not quite so side-effect free.
However, our goal is to preserve historical v1 semantic when possible
regardless of whether it made sense.
Note that jsontext.Decoder.InputOffset consistently always reports
the end of the previous token. Users can explicitly choose the
exact position they want by inspecting the UnreadBuffer.
Fixes #75468
Change-Id: I1e946e83c9d29dfc09f2913ff8d6b2b80632f292
Reviewed-on: https://go-review.googlesource.com/c/go/+/703856 Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Junyang Shao <shaojunyang@google.com>