fbt: source collection improvements (#3181)

* fbt: reduced amount of redundant compilation units
* fbt: added GatherSources() method which can reject source paths starting with "!" in sources list; optimized apps' source lists
* docs: updated on path exclusion for `sources`
* apps: examples: fixed example_advanced_plugins source list
* docs: more details on `sources`; apps: narrower sources lists

applications/main/ibutton/application.fam

@@ -17,5 +17,6 @@ App(
     apptype=FlipperAppType.STARTUP,
     targets=["f7"],
     entry_point="ibutton_on_system_start",
+    sources=["ibutton_cli.c"],
     order=60,
 )