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>

client/freedesktop/freedesktop_test.go

@@ -13,12 +13,12 @@ func TestEscape(t *testing.T) {
 		name, input, want string
 	}{
 		{
-			name:  "no illegal chars",
+			name:  "no-illegal-chars",
 			input: "/home/user",
 			want:  "/home/user",
 		},
 		{
-			name:  "empty string",
+			name:  "empty-string",
 			input: "",
 			want:  "\"\"",
 		},
@@ -38,12 +38,12 @@ func TestEscape(t *testing.T) {
 			want:  "\"\n\"",
 		},
 		{
-			name:  "double quote",
+			name:  "double-quote",
 			input: "\"",
 			want:  "\"\\\"\"",
 		},
 		{
-			name:  "single quote",
+			name:  "single-quote",
 			input: "'",
 			want:  "\"'\"",
 		},
@@ -53,12 +53,12 @@ func TestEscape(t *testing.T) {
 			want:  "\"\\\\\"",
 		},
 		{
-			name:  "greater than",
+			name:  "greater-than",
 			input: ">",
 			want:  "\">\"",
 		},
 		{
-			name:  "less than",
+			name:  "less-than",
 			input: "<",
 			want:  "\"<\"",
 		},
@@ -93,7 +93,7 @@ func TestEscape(t *testing.T) {
 			want:  "\"*\"",
 		},
 		{
-			name:  "question mark",
+			name:  "question-mark",
 			input: "?",
 			want:  "\"?\"",
 		},
@@ -103,12 +103,12 @@ func TestEscape(t *testing.T) {
 			want:  "\"#\"",
 		},
 		{
-			name:  "open paren",
+			name:  "open-paren",
 			input: "(",
 			want:  "\"(\"",
 		},
 		{
-			name:  "close paren",
+			name:  "close-paren",
 			input: ")",
 			want:  "\")\"",
 		},
@@ -118,17 +118,17 @@ func TestEscape(t *testing.T) {
 			want:  "\"\\`\"",
 		},
 		{
-			name:  "char without escape",
+			name:  "char-without-escape",
 			input: "/home/user\t",
 			want:  "\"/home/user\t\"",
 		},
 		{
-			name:  "char with escape",
+			name:  "char-with-escape",
 			input: "/home/user\\",
 			want:  "\"/home/user\\\\\"",
 		},
 		{
-			name:  "all illegal chars",
+			name:  "all-illegal-chars",
 			input: "/home/user" + needsEscape,
 			want:  "\"/home/user \t\n\\\"'\\\\><~|&;\\$*?#()\\`\"",
 		},