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/project_template/.clangd

@@ -0,0 +1,17 @@
+CompileFlags:
+    Add: 
+        - -Wno-unknown-warning-option
+        - -Wno-format
+    Remove: 
+        - -mword-relocations
+
+Diagnostics:
+    ClangTidy:
+        FastCheckFilter: None
+
+---
+
+If:
+    PathMatch: .*\.h
+Diagnostics:
+    UnusedIncludes: None