[clang-tools-extra] [clang-doc] Add basic e2e test (PR #93928)

[Paul Kirth via cfe-commits]

================
@@ -0,0 +1,17 @@
+[
+  {
+    "directory": "$test_dir/build",
+    "command": "clang++ -o Calculator.o -I../include $test_dir/src/Calculator.cpp",
----------------
ilovepi wrote:

```suggestion
    "command": "clang++ -o Calculator.o -I../include ../src/Calculator.cpp",
```
This can be relative too. Same in other lines.

https://github.com/llvm/llvm-project/pull/93928