vscode-clangd extension does not work

[spoenemann]

Description

The vscode-clangd extension fails to activate with an exception.

Marketplace:
https://marketplace.visualstudio.com/items?itemName=llvm-vs-code-extensions.vscode-clangd

Source:
https://github.com/llvm/llvm-project/tree/master/clang-tools-extra/clangd/clients/clangd-vscode

Trace:

root INFO [hosted-plugin: 5551] PLUGIN_HOST(5551): PluginManagerExtImpl/loadPlugin(/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/out/src/extension)
root INFO [hosted-plugin: 5551] Clang Language Server is now active!
root ERROR [hosted-plugin: 5551] Promise rejection not handled in one second: TypeError: vscode_1.languages.registerSelectionRangeProvider is not a function , reason: TypeError: vscode_1.languages.registerSelectionRangeProvider is not a function
With stack trace: TypeError: vscode_1.languages.registerSelectionRangeProvider is not a function
    at SelectionRangeFeature.registerLanguageProvider (/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/node_modules/vscode-languageclient/lib/selectionRange.js:51:36)
    at SelectionRangeFeature.register (/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/node_modules/vscode-languageclient/lib/client.js:709:33)
    at SelectionRangeFeature.initialize (/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/node_modules/vscode-languageclient/lib/selectionRange.js:29:14)
    at ClangdLanguageClient.initializeFeatures (/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/node_modules/vscode-languageclient/lib/client.js:2462:21)
    at connection.initialize.then (/tmp/vscode-unpacked/llvm-vs-code-extensions.vscode-clangd-0.0.21.vsix/extension/node_modules/vscode-languageclient/lib/client.js:2147:18)

Reproduction Steps

• Add the extension as described in the Wiki.
• Use the "Manually activate clangd extension" to activate it (it is not activated by default on .cpp files)

OS and Theia version: macOS 10.15.3, commit 5e45d2b on master branch

Diagnostics:
The extension is using vscode-languageclient version 6.1.0, which expects vscode ^1.41.0.

[akosyakov]

Duplicate of #6623