hclwrite: Formatter to put spaces before colons

The symmetrical spaces around colons in conditionals are important for
familiarity with C-like languages, so we'll instead accept spaces around
colons in our HCL2-unique "for expression" construct.

hclwrite/format.go

@@ -316,10 +316,6 @@ func spaceAfterToken(subject, before, after *Token) bool {
 		}
 		return true
 
-	case after.Type == hclsyntax.TokenColon:
-		// Never spaces before colons
-		return false
-
 	// In the unlikely event that an interpolation expression is just
 	// a single object constructor, we'll put a space between the ${ and
 	// the following { to make this more obvious, and then the same

hclwrite/format_test.go

@@ -107,17 +107,21 @@ foo(
 )
 `,
 		},
+		{
+			`a?b:c`,
+			`a ? b : c`,
+		},
 		{
 			`[ [ ] ]`,
 			`[[]]`,
 		},
 		{
-			`[for x in y: x]`,
-			`[for x in y: x]`,
+			`[for x in y : x]`,
+			`[for x in y : x]`,
 		},
 		{
-			`[for x in [y]: x]`,
-			`[for x in [y]: x]`,
+			`[for x in [y] : x]`,
+			`[for x in [y] : x]`,
 		},
 		{
 			`