[clangd][vscode] Update vscode lsp dependencies to pickup the new changes in LSP v3.15.0.

Summary: This would enable the newly-added semantic selection feature in vscode.

Reviewers: usaxena95

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67964

llvm-svn: 372970