chore: update issue templates (#14338)

Author: josephperrott

.github/ISSUE_TEMPLATE/bug.md

@@ -0,0 +1,21 @@
+---
+name: Bug
+about: Report a bug found in Angular Material, CDK or our docs
+
+---
+
+#### What is the expected behavior?
+
+
+#### What is the current behavior?
+
+
+#### What are the steps to reproduce?
+Providing a StackBlitz reproduction is the *best* way to share your issue. <br/>
+StackBlitz starter: https://goo.gl/wwnhMV<br/>
+
+
+#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
+
+
+#### Is there anything else we should know?

.github/ISSUE_TEMPLATE/feature---proposal.md

@@ -0,0 +1,13 @@
+---
+name: Feature / Proposal
+about: Propose a new feature for Angular Material or CDK
+
+---
+
+#### Please describe the feature you would like to request.
+
+
+#### What is the use-case or motivation for this proposal?
+
+
+#### Is there anything else we should know?

.github/ISSUE_TEMPLATE/feature-proposal.md

@@ -0,0 +1,13 @@
+---
+name: Feature/Proposal
+about: Propose a new feature for Angular Material or CDK
+
+---
+
+#### Please describe the feature you would like to request.
+
+
+#### What is the use-case or motivation for this proposal?
+
+
+#### Is there anything else we should know?

.github/ISSUE_TEMPLATE/feature.md

@@ -0,0 +1,13 @@
+---
+name: Feature
+about: Propose a new feature for Angular Material or CDK
+
+---
+
+#### Please describe the feature you would like to request.
+
+
+#### What is the use-case or motivation for this proposal?
+
+
+#### Is there anything else we should know?