Fix gitignore

- `*build*/` is not needed because Meson puts a .gitignore in builddir
already.

- `meson/` why?

- `/gst*` is too wide, it includes e.g. gst-env.py, list symlinks
explicitly instead.

- `subprojects/*` excludes all .wrap files, and `!subprojects/gst*` is
not enough because e.g. `macos-bison-binary` is still ignored. Instead
ignore only directories except those we include in our git repository.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/969>

.gitignore

@@ -1,16 +1,47 @@
-*build*/
 cscope.in.out
 cscope.out
 cscope.po.out
-libnice
 __pycache__
-meson/
 prefix/
-pygobject
 .gdbinit
 
-/gst*
-subprojects/*
-!subprojects/gst*
-subprojects/gst-plugins-rs/
-subprojects/gstreamer-rs/
+# Symlinks
+/gstreamer
+/gst-plugins-base
+/gst-plugins-good
+/libnice
+/gst-plugins-bad
+/gst-plugins-ugly
+/gst-libav
+/gst-rtsp-server
+/gst-devtools
+/gst-integration-testsuites
+/gst-editing-services
+/gstreamer-vaapi
+/gst-omx
+/gstreamer-sharp
+/pygobject
+/gst-python
+/gst-examples
+/gst-plugins-rs
+
+subprojects/*/
+!subprojects/gst-devtools
+!subprojects/gst-docs
+!subprojects/gst-editing-services
+!subprojects/gst-examples
+!subprojects/gst-integration-testsuites
+!subprojects/gst-libav
+!subprojects/gst-omx
+!subprojects/gst-plugins-bad
+!subprojects/gst-plugins-base
+!subprojects/gst-plugins-good
+!subprojects/gst-plugins-ugly
+!subprojects/gst-python
+!subprojects/gstreamer
+!subprojects/gstreamer-sharp
+!subprojects/gstreamer-vaapi
+!subprojects/gst-rtsp-server
+!subprojects/macos-bison-binary
+!subprojects/win-flex-bison-binaries
+!subprojects/win-nasm