CI/Flatpak: Improve install behaviour

Use "standard" install path.

scripts/flatpak/modules/21-libbacktrace.yaml

@@ -10,7 +10,7 @@ build-options:
 sources:
   - type: git
     url: "https://github.com/ianlancetaylor/libbacktrace.git"
-    commit: "ad106d5fdd5d960bd33fae1c48a351af567fd075"
+    commit: "86885d14049fab06ef8a33aac51664230ca09200"
 cleanup:
   - /include
   - /lib/*.a

scripts/flatpak/org.duckstation.DuckStation.yaml

@@ -43,7 +43,6 @@ modules:
   - name: duckstation
     buildsystem: cmake-ninja
     builddir: true
-    no-make-install: true
     build-options:
       # Preserve debug information, it is needed for backtraces.
       strip: false
@@ -60,7 +59,11 @@ modules:
         - "-DCMAKE_BUILD_TYPE=Release"
 
         # We're not running tests as part of the flatpak build.
-        - '-DBUILD_TESTS=OFF'
+        - "-DBUILD_TESTS=OFF"
+
+        # Install to /app/bin, use /app/lib for dependencies.
+        - "-DALLOW_INSTALL=ON"
+        - "-DINSTALL_SELF_CONTAINED=OFF"
 
         # Make sure we're using ThinLTO.
         - "-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON"
@@ -74,9 +77,6 @@ modules:
         path: ../..
 
     post-install:
-      # Copy the binary distribution.
-      - "cp -a bin \"${FLATPAK_DEST}\""
-
       # Manually copy desktop file/metadata, it's not done as part of the regular build.
       - >-
         install -Dm644