go/printer: do not add a space after comment in template part

Currently in the Go printer, the code below is already formatted:

a(sth /*l*/)

This change aligns this behaviour for template parts, before this
change, following code:

"\{sth /*l*/}"

got formatted into:

"\{sth /*l*/ }"

now it is unchanged.

printer/testdata/tgo/3.formatted

@@ -133,16 +133,16 @@ func test(sth string) {
 	"test\{sth}" /*test*/
 
 	"test \{ /*comment*/ test}"
-	"test \{test /*c*/ }"
-	"test \{ /*c*/ test /*c*/ }"
+	"test \{test /*c*/}"
+	"test \{ /*c*/ test /*c*/}"
 
 	"test" /*test*/
 
 	"test \{ /*comment*/ test}" /*test*/
 
-	"test \{test /*c*/ }" /*test*/
+	"test \{test /*c*/}" /*test*/
 
-	"test \{ /*c*/ test /*c*/ }" /*test*/
+	"test \{ /*c*/ test /*c*/}" /*test*/
 
 	"hello \{ /*c*/ sth}"
 	/*test*/ "hello \{ /*c*/ sth}"

printer/tgo.go

@@ -130,11 +130,14 @@ func (p *printer) templateLiteralExpr(x *ast.TemplateLiteralExpr) {
 	p.setPos(x.OpenPos)
 	p.print(x.Strings[0])
 	for i := range x.Parts {
-		p.print("\\{")
-		p.setPos(x.Parts[i].Pos())
+		p.print("\\", token.LBRACE)
+		p.setPos(x.Parts[i].LBrace)
 		p.expr(stripParensAlways(x.Parts[i].X))
-		p.setPos(x.Parts[i].End())
-		p.print("}")
+		p.setPos(x.Parts[i].RBrace)
+		if p.mode&noExtraLinebreak != 0 || p.mode&noExtraBlank != 0 {
+			panic("unreachable")
+		}
+		p.print(noExtraLinebreak|noExtraBlank, token.RBRACE, noExtraLinebreak|noExtraBlank)
 		p.print(x.Strings[i+1])
 	}
 }