Change issue templates to not hide stuff by default

Using the "details" tag for all templates is excessive since most of the
time, the compilation output is quite small, and not seeing it at a
glance can be confusing. Only stack traces are worth hiding.

Author: smarter

.github/ISSUE_TEMPLATE/bug.md

@@ -13,12 +13,10 @@ assignees: ''
 println("hello, world")
 ```
 
-<details>
-<summary>Compilation output</summary>
+## Compilation output
 
 ```scala
-# TODO add compilation output here
+// TODO add compilation output here
 ```
-</details>
 
 ## expectation

.github/ISSUE_TEMPLATE/crash.md

@@ -13,11 +13,10 @@ assignees: ''
 println("hello, world")
 ```
 
-
+## Stack trace (click arrow to expand)
 <details>
-<summary>Stack trace</summary>
 
 ```scala
-# TODO add stack trace here
+// TODO add stack trace here
 ```
 </details>

.github/ISSUE_TEMPLATE/other-issue.md

@@ -13,12 +13,10 @@ assignees: ''
 println("hello, world")
 ```
 
-<details>
-<summary>Compilation output</summary>
+## Compilation output
 
 ```scala
-# TODO add compilation output here
+// TODO add compilation output here
 ```
-</details>
 
 ## expectation