Create issue template for feature depreaction

Author: sbc100

.github/ISSUE_TEMPLATE/feature_depreaction.md

@@ -0,0 +1,23 @@
+---
+name: Feature deprecation
+about: Use this template for removal of features from emscripten.
+title: 'Deprection proposal for <FEATURE>'
+labels: 'depreaction'
+assignees: ''
+
+---
+
+Tracking issue for the deprecation and removal of <FEATURE>.
+
+The process for deprecating and removing features from emscripten is laid out out in https://github.com/emscripten-core/emscripten/blob/main/docs/process.md#deprecating-settings-and-features.
+
+At any point in the process we may decide to delay or abort the deprecation and close this issue.
+
+Deprecation checklist:
+
+- [ ] Open an issue (this)
+- [ ] Perform global search for usage in public repos
+- [ ] Send message to emscripten-discuss
+- [ ] Add "deprecation" warning to emcc
+- [ ] Wait at least 4 releases or 2 months
+- [ ] Remove feature from codebase