Support new "textDocument/inlineCompletion" LSP completion API

[JeremyWeed]

Is your feature request related to a problem? Please describe.

The next release of the LSP protocol (3.18.0) will support this new method, which is designed to better facilitate multi-line based completions from AI-based completion frameworks. Given this will be the official way to support clients like this, it'd be great to support this new method. Open source LSP clients have already begun to support this API (example), and this would allow users outside of the VSCode/Jetbrains ecosystem to integrate well with this server.

Describe the solution you'd like

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#textDocument_inlineCompletion is supported by the CodeWhisperer LSP server

[justinmk3]

related:

• Q/codewhisperer does not support LSP standard "textDocument/completion" method #724
• feat(amazonq): implement basic server for standard LSP completion API #739