database/sql: rewrite Null[T].Value method, update doc for Null[T]
Update doc for Null[T] to clarify that T should be one of the types
accepted by driver.Value.
Modify the Value() method of Null[T]:
1) recognize T implementing driver.Valuer interface and invoke it.
2) use the DefaultParameterConverter to convert native types that
are not directly supported as driver.Value types.
Fixes #69728
Fixes #69837
Change-Id: Iba782c878b2bde168125f5390abf319b88424149
GitHub-Last-Rev:
3df182d23dd57bd04828c3e9bd0c5222d8bef152
GitHub-Pull-Request: golang/go#69938
Reviewed-on: https://go-review.googlesource.com/c/go/+/620858
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>