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>

ipn/serve_test.go

@@ -283,11 +283,11 @@ func TestExpandProxyTargetDev(t *testing.T) {
 		wantErr          bool
 	}{
 		{name: "port-only", input: "8080", expected: "http://127.0.0.1:8080"},
-		{name: "hostname+port", input: "localhost:8080", expected: "http://localhost:8080"},
+		{name: "hostname-and-port", input: "localhost:8080", expected: "http://localhost:8080"},
 		{name: "no-change", input: "http://127.0.0.1:8080", expected: "http://127.0.0.1:8080"},
 		{name: "include-path", input: "http://127.0.0.1:8080/foo", expected: "http://127.0.0.1:8080/foo"},
 		{name: "https-scheme", input: "https://localhost:8080", expected: "https://localhost:8080"},
-		{name: "https+insecure-scheme", input: "https+insecure://localhost:8080", expected: "https+insecure://localhost:8080"},
+		{name: "https-insecure-scheme", input: "https+insecure://localhost:8080", expected: "https+insecure://localhost:8080"},
 		{name: "change-default-scheme", input: "localhost:8080", defaultScheme: "https", expected: "https://localhost:8080"},
 		{name: "change-supported-schemes", input: "localhost:8080", defaultScheme: "tcp", supportedSchemes: []string{"tcp"}, expected: "tcp://localhost:8080"},
 		{name: "remote-target", input: "https://example.com:8080", expected: "https://example.com:8080"},