toolchain: v38; clangd as default language server (#3774)

* libs: removed cxxheaderparser submodule, expecting one from toolchain
* toolchain: v38
* vscode: now using clangd from toolchain
* vscode: clangd path in config is now generated by fbt
* vscode, fbt: improved clangd path generation
* fbt: fixed LANG_SERVER handling; switched to clangd as default
* vscode: removed deprecated options from config
* ufbt: project template: updated clang-format, added clangd config
* ufbt: now using clangd as default language server
* ufbt: now using clangd as default language server

.vscode/example/settings.json.tmpl

@@ -0,0 +1,22 @@
+{
+    "workbench.tree.indent": 12,
+    "cortex-debug.enableTelemetry": false,
+    "cortex-debug.variableUseNaturalFormat": true,
+    "cortex-debug.armToolchainPath": "${workspaceFolder}/toolchain/current/bin",
+    "cortex-debug.openocdPath": "${workspaceFolder}/toolchain/current/bin/openocd",
+    "cortex-debug.gdbPath": "${workspaceFolder}/toolchain/current/bin/arm-none-eabi-gdb-py3",
+    "editor.formatOnSave": true,
+    "files.associations": {
+        "*.scons": "python",
+        "SConscript": "python",
+        "SConstruct": "python",
+        "*.fam": "python"
+    },
+    "clangd.path": "${workspaceFolder}/toolchain/current/bin/clangd@FBT_PLATFORM_EXECUTABLE_EXT@",
+    "clangd.arguments": [
+        "--query-driver=**/arm-none-eabi-*",
+        "--compile-commands-dir=${workspaceFolder}/build/latest",
+        "--clang-tidy",
+        "--header-insertion=never"
+    ]
+}