Replace existing issue templates with issue forms

Issue forms provide better guidance when creating issues, especially
for people less familiar with GitHub issue creation.

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,43 @@
+name: Feature request
+description: Request a feature to be added or improved in DuckStation
+body:
+
+- type: markdown
+  attributes:
+    value: |
+      **Please read before creating a new feature request:**
+      1. Make sure there is not already an issue for this feature request by [searching in **both** open and closed issues](https://github.com/stenzek/duckstation/issues?q=is%3Aissue+sort%3Aupdated-desc+).
+      2. Please open **one issue per requested feature**. Do not cram several unrelated feature requests in a single issue, as this makes it harder for contributors to track what's being worked on.
+      3. Please post your feature request in English, as this is the only language spoken by the developers. The [Discord server](https://discord.gg/Buktv3t) has many helpful people if you need help translating.
+      4. Issues about the libretro core will be deleted (you will be blocked from the repository if you create such an issue). That core is not DuckStation, it is a broken fork, and has nothing to do with us.
+
+- type: textarea
+  attributes:
+    label: Problem statement
+    description: |
+      Is your feature request related to a problem? Please describe.
+    placeholder: Example - "I'm always frustrated when […]"
+  validations:
+    required: true
+
+- type: textarea
+  attributes:
+    label: Proposed solution
+    description: |
+      A clear and concise description of what you want to happen.
+  validations:
+    required: true
+
+- type: textarea
+  attributes:
+    label: Alternatives considered
+    description: |
+      Describe alternatives you've considered.
+  validations:
+    required: true
+
+- type: textarea
+  attributes:
+    label: Additional context
+    description: |
+      Add any other context about the problem or proposed feature here.