[clangd] ArgumentLists not used for lambda call auto-completion

[olemayu]

Auto-completing lambda always inserts FullPlaceholders, ignoring the user config.

auto lambda = [](int a, int b) {};

lamda(int a, int b) // auto-completion result

clangd version: 21.0.0

[llvmbot]

@llvm/issue-subscribers-clangd

Author: None (olemayu)

Auto-completing lambda *always* inserts **FullPlaceholders**, ignoring the user config.

auto lambda = [](int a, int b) {};

lamda(int a, int b) // auto-completion result

clangd version: 21.0.0