Rename, clean up boards/variants (#21655)

* Consolidate variant scripts
* Rename Marlin-local boards
* Simplify variants where possible
* Rename variants
* CHITU_F103 and MEEB_3DP: Maple platform `platformio-build-stm32f1.py` uses the 'board' name, not 'board_build.variant' so folder names match 'board' and not `board_build.variant`.

buildroot/share/PlatformIO/boards/marlin_malyanM200.json

@@ -0,0 +1,35 @@
+{
+  "build": {
+    "core": "maple",
+    "cpu": "cortex-m3",
+    "extra_flags": "-DARDUINO_GENERIC_STM32F103C -DMCU_STM32F103CB",
+    "f_cpu": "72000000L",
+    "hwids": [
+        ["0x1EAF", "0x0003"],
+        ["0x1EAF", "0x0004"]
+    ],
+    "ldscript": "jtagOffset.ld",
+    "mcu": "stm32f103cb",
+    "variant": "malyanM200",
+    "vec_tab_addr": "0x8002000"
+  },
+  "debug": {
+    "jlink_device": "STM32F103CB",
+    "openocd_target": "stm32f1x",
+    "svd_path": "STM32F103xx.svd"
+  },
+  "platform": "ststm32",
+  "frameworks": ["arduino"],
+  "name": "Malyan STM32F103CB (20k RAM. 128k Flash)",
+  "upload": {
+    "disable_flushing": false,
+    "maximum_ram_size": 20480,
+    "maximum_size": 131072,
+    "protocol": "serial",
+    "require_upload_port": true,
+    "use_1200bps_touch": false,
+    "wait_for_upload_port": false
+  },
+  "url": "https://www.st.com/content/st_com/en/products/microcontrollers/stm32-32-bit-arm-cortex-mcus/stm32f1-series/stm32f103/stm32f103cb.html",
+  "vendor": "Generic"
+}