go/types, types2: missing error for shifts by huge untyped integers

[griesemer]

Per the spec:

The right operand in a shift expression must have integer type or be an untyped constant representable by a value of type uint.

for the following code

package p

var x int
var _ = x << 100000000000000000000

go/types (and types2) should report an error but doesn't.

For reference, cmd/compile reports

main.go:4:11: constant 100000000000000000000 overflows uint

[griesemer]

cc: @findleyr

[gopherbot]

Change https://golang.org/cl/283872 mentions this issue: [dev.typeparams] cmd/compile/internal/types2: untyped shift counts must fit into uint

[gopherbot]

Change https://golang.org/cl/291316 mentions this issue: [dev.regabi] go/types: untyped shift counts must fit into uint

[findleyr]

Now that these changes are merged to master, I believe this can be closed. @griesemer please reopen if I'm misunderstanding something.