docs(PULL_REQUEST_TEMPLATE.md): reorganize and improve the pull request template

Closes #7921

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,24 +1,32 @@
-* **Please check if the PR fulfills these requirements**
+**Please check if the PR fulfills these requirements**
 - [ ] The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit-message-format
 - [ ] Tests for the changes have been added (for bug fixes / features)
 - [ ] Docs have been added / updated (for bug fixes / features)
 
 
-* **What kind of change does this PR introduce?** (Bug fix, feature, docs update, ...)
+**What kind of change does this PR introduce?** (Bug fix, feature, docs update, ...)
+- [ ] Bugfix
+- [ ] Feature
+- [ ] Code style update (formatting, local variables)
+- [ ] Refactoring (no functional changes, no api changes)
+- [ ] Build related changes
+- [ ] CI related changes
+- [ ] Other... Please describe:
+
+**What is the current behavior?** (You can also link to an open issue here)
 
 
 
-* **What is the current behavior?** (You can also link to an open issue here)
+**What is the new behavior?**
 
 
 
-* **What is the new behavior (if this is a feature change)?**
+**Does this PR introduce a breaking change?**
+- [ ] Yes
+- [ ] No
+
+If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...
 
 
-
-* **Does this PR introduce a breaking change?** (What changes might users need to make in their application due to this PR?)
-
-
-
-* **Other information**:
+**Other information**: