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

scripts/ufbt/SConstruct

@@ -403,6 +403,9 @@ for template_file in project_template_dir.Dir(".vscode").glob("*"):
                 "@UFBT_FIRMWARE_ELF@": PosixPathWrapper.fix_path(
                     dist_env["FW_ELF"].abspath
                 ),
+                "@UFBT_TOOLCHAIN_CLANGD@": PosixPathWrapper.fix_path(
+                    dist_env.WhereIs("clangd")
+                ),
             },
         )
     )