Support angular control flow (#15606)

Co-authored-by: dweizhe <d.weizhe@anyong.com.tw>
Co-authored-by: fisker <lionkay@gmail.com>

tests/format/angular/control-flow/defer.html

@@ -0,0 +1,68 @@
+@defer (when isCheckedDefer()) {
+<app-c1/>
+}
+@placeholder {
+<span>Placeholder</span>
+}
+@error {
+<span>Error</span>
+}
+@loading(minimum 1s) {
+<span>Loading...</span>
+}
+
+
+@defer (on interaction) {
+<span>Clicked</span>
+}
+@placeholder {
+<span>Placeholder (click on it!)</span>
+}
+
+
+@defer (on hover) {
+<span>Hovered</span>
+}
+@placeholder {
+<span>Placeholder (hover it!)</span>
+}
+
+
+@defer (on idle) {
+<span>Browser has reached an idle state</span>
+}
+@placeholder {
+<span>Placeholder</span>
+}
+
+
+@defer (on timer(5s)) {
+<span>Visible after 5s</span>
+}
+@placeholder {
+<span>Placeholder</span>
+}
+
+
+@defer (on viewport) {
+<app-c2 text="The block entered the viewport"/>
+}
+@placeholder {
+<span>Placeholder</span>
+}
+
+
+@defer (on interaction; prefetch on hover) {
+<app-c3/>
+}
+@placeholder {
+<span>Placeholder (hover it, then click on it!)</span>
+}
+
+
+@defer (on interaction; prefetch on hover) {
+<app-c3/>
+}
+@placeholder {
+<span>Placeholder (hover it, then click on it!)</span>
+}