encoding/json, text/template: use reflect.Value.Equal instead of ==

This change applies a fix for a reflect.Value incorrect comparison
using "==" or reflect.DeepEqual.
This change is a precursor to the change that'll bring in the
static analyzer "reflectvaluecompare", by ensuring that all tests
pass beforehand.

Updates #43993

Change-Id: I6c47eb0a1de6353ac7495cb8cb49b318b7ebba56
Reviewed-on: https://go-review.googlesource.com/c/go/+/626116
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: odeke-em

Diff for: src/encoding/json/decode.go

@@ -472,7 +472,7 @@ func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnm
 		// Prevent infinite loop if v is an interface pointing to its own address:
 		//     var v any
 		//     v = &v
-		if v.Elem().Kind() == reflect.Interface && v.Elem().Elem() == v {
+		if v.Elem().Kind() == reflect.Interface && v.Elem().Elem().Equal(v) {
 			v = v.Elem()
 			break
 		}

Diff for: src/text/template/exec.go

@@ -810,7 +810,7 @@ func (s *state) evalCall(dot, fun reflect.Value, isBuiltin bool, node parse.Node
 				return v
 			}
 		}
-		if final != missingVal {
+		if !final.Equal(missingVal) {
 			// The last argument to and/or is coming from
 			// the pipeline. We didn't short circuit on an earlier
 			// argument, so we are going to return this one.