cmd/vet: add subtestnames analyzer; fix all existing violations

Add a new vet analyzer that checks t.Run subtest names don't contain
characters requiring quoting when re-running via "go test -run". This
enforces the style guide rule: don't use spaces or punctuation in
subtest names.

The analyzer flags:
- Direct t.Run calls with string literal names containing spaces,
  regex metacharacters, quotes, or other problematic characters
- Table-driven t.Run(tt.name, ...) calls where tt ranges over a
  slice/map literal with bad name field values

Also fix all 978 existing violations across 81 test files, replacing
spaces with hyphens and shortening long sentence-like names to concise
hyphenated forms.

Updates #19242

Change-Id: Ib0ad96a111bd8e764582d1d4902fe2599454ab65
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/dnstype/dnstype_test.go

@@ -33,13 +33,13 @@ func TestResolverEqual(t *testing.T) {
 			want: true,
 		},
 		{
-			name: "nil vs non-nil",
+			name: "nil-vs-non-nil",
 			a:    nil,
 			b:    &Resolver{},
 			want: false,
 		},
 		{
-			name: "non-nil vs nil",
+			name: "non-nil-vs-nil",
 			a:    &Resolver{},
 			b:    nil,
 			want: false,
@@ -51,13 +51,13 @@ func TestResolverEqual(t *testing.T) {
 			want: true,
 		},
 		{
-			name: "not equal addrs",
+			name: "not-equal-addrs",
 			a:    &Resolver{Addr: "dns.example.com"},
 			b:    &Resolver{Addr: "dns2.example.com"},
 			want: false,
 		},
 		{
-			name: "not equal bootstrap",
+			name: "not-equal-bootstrap",
 			a: &Resolver{
 				Addr:                "dns.example.com",
 				BootstrapResolution: []netip.Addr{netip.MustParseAddr("8.8.8.8")},
@@ -69,13 +69,13 @@ func TestResolverEqual(t *testing.T) {
 			want: false,
 		},
 		{
-			name: "equal UseWithExitNode",
+			name: "equal-UseWithExitNode",
 			a:    &Resolver{Addr: "dns.example.com", UseWithExitNode: true},
 			b:    &Resolver{Addr: "dns.example.com", UseWithExitNode: true},
 			want: true,
 		},
 		{
-			name: "not equal UseWithExitNode",
+			name: "not-equal-UseWithExitNode",
 			a:    &Resolver{Addr: "dns.example.com", UseWithExitNode: true},
 			b:    &Resolver{Addr: "dns.example.com", UseWithExitNode: false},
 			want: false,