Bump golangci-lint and (max) Go versions (#219)

Lint is failing with some inscrutable panic (on a commit with no code
changes). Let's try bumping the version in case they fixed it.

Additionally, the new version's github action uses Go 1.19, which means
it pulls in gofmt updates to match the new [doc-comment formatting rules][1].
So I added Go 1.19 to our list of versions to test (fixes #216)
and updated some of our doc-comments to format better in the
new world (mostly using the new link syntax).

[1]: https://go.dev/doc/comment

Test plan: make lint

generate/types.go

@@ -186,11 +186,11 @@ func (field *goStructField) Selector() string {
 }
 
 // unmarshaler returns:
-// - the name of the function to use to unmarshal this field
-// - true if this is a fully-qualified name (false if it is a package-local
-//   unqualified name)
-// - true if we need to generate an unmarshaler at all, false if the default
-//   behavior will suffice
+//   - the name of the function to use to unmarshal this field
+//   - true if this is a fully-qualified name (false if it is a package-local
+//     unqualified name)
+//   - true if we need to generate an unmarshaler at all, false if the default
+//     behavior will suffice
 func (field *goStructField) unmarshaler() (qualifiedName string, needsImport bool, needsUnmarshaler bool) {
 	switch typ := field.GoType.Unwrap().(type) {
 	case *goOpaqueType:
@@ -214,9 +214,9 @@ func (field *goStructField) Unmarshaler(g *generator) (string, error) {
 }
 
 // marshaler returns:
-// - the fully-qualified name of the function to use to marshal this field
-// - true if we need to generate an marshaler at all, false if the default
-//   behavior will suffice
+//   - the fully-qualified name of the function to use to marshal this field
+//   - true if we need to generate an marshaler at all, false if the default
+//     behavior will suffice
 func (field *goStructField) marshaler() (qualifiedName string, needsImport bool, needsMarshaler bool) {
 	switch typ := field.GoType.Unwrap().(type) {
 	case *goOpaqueType:
@@ -273,17 +273,21 @@ type selector struct {
 // and the paths to reach them (via those embeds), but with different
 // visibility rules for conflicting fields than Go.
 //
-// (Before you read further, now's a good time to review Go's rules:
-// https://golang.org/ref/spec#Selectors. Done? Good.)
+// (Before you read further, now's a good time to review [Go's rules].
+// Done?  Good.)
 //
 // To illustrate the need, consider the following query:
+//
 //	fragment A on T { id }
 //	fragment B on T { id }
 //	query Q { t { ...A ...B } }
+//
 // We generate types:
+//
 //	type A struct { Id string `json:"id"` }
 //	type B struct { Id string `json:"id"` }
 //	type QT struct { A; B }
+//
 // According to Go's embedding rules, QT has no field Id: since QT.A.Id and
 // QT.B.Id are at equal depth, neither wins and gets promoted.  (Go's JSON
 // library uses similar logic to decide which field to write to JSON, except
@@ -307,7 +311,10 @@ type selector struct {
 // practice, hopefully, they all match, but validating that is even more work
 // for a fairly rare case.)  This function returns, for each JSON-name, the Go
 // field we want to use.  In the example above, it would return:
+//
 //	[]selector{{<goStructField for QT.A.Id>, "A.Id"}}
+//
+// [Go's rules]: https://golang.org/ref/spec#Selectors
 func (typ *goStructType) FlattenedFields() ([]*selector, error) {
 	seenJSONNames := map[string]bool{}
 	retval := make([]*selector, 0, len(typ.Fields))