fbt fixes & improvements (#1490)

* fbt: minimal USB flash mode; scripts: faster storage.py with larger chunks
* fbt: fixed creation of temporary file nodes confusing scons
* docs: removed refs to --with-updater
* fbt: removed splashscreen from minimal update package
* fbt: renamed dist arguments for consistency
* docs: fixed updater_debug target
* fbt: separate target for generating compilation_database.json without building the code.
* fbt: added `jflash` target for programming over JLink probe; refactored usb flashing targets
* fbt: building updater_app in unit_tests configuration
* fbt: fixed reset behavior after flashing with J-Link
* fbt: generating .map file for firmware binary & external apps
* fbt/core: moved library contents before apps code

Co-authored-by: あく <alleteam@gmail.com>

site_scons/site_tools/jflash.py

@@ -0,0 +1,27 @@
+from SCons.Builder import Builder
+from SCons.Defaults import Touch
+
+
+def generate(env):
+    env.SetDefault(
+        JFLASH="JFlash" if env.subst("$PLATFORM") == "win32" else "JFlashExe",
+        JFLASHFLAGS=[
+            "-auto",
+            "-exit",
+        ],
+        JFLASHCOM="${JFLASH} -openprj${JFLASHPROJECT} -open${SOURCE},${JFLASHADDR} ${JFLASHFLAGS}",
+    )
+    env.Append(
+        BUILDERS={
+            "JFlash": Builder(
+                action=[
+                    "${JFLASHCOM}",
+                    Touch("${TARGET}"),
+                ],
+            ),
+        }
+    )
+
+
+def exists(env):
+    return True