Support textDocument/inlineCompletion request from 3.18

[rcjsuen]

I used #30 as an example for adding support for the new textDocument/inlineCompletion request introduced in 3.18. @tliron I know copy/pasting isn't the best of ideas but it can help get people unblocked for now. What do you think?

I tested it by having Visual Studio Code connect to the language server below and triggering the textDocument/inlineCompletion request from the editor.

package main

import (
	"github.com/tliron/commonlog"
	"github.com/tliron/glsp"
	protocol316 "github.com/tliron/glsp/protocol_3_16"
	protocol317 "github.com/tliron/glsp/protocol_3_17"
	protocol318 "github.com/tliron/glsp/protocol_3_18"
	"github.com/tliron/glsp/server"
)

const lsName = "my language"

var (
	version string = "0.0.1"
	handler protocol318.Handler
)

func main() {
	// This increases logging verbosity (optional)
	commonlog.Configure(1, nil)

	handler = protocol318.Handler{
		Initialize: initialize,
		TextDocumentInlineCompletion: func(context *glsp.Context, params *protocol318.InlineCompletionParams) (any, error) {
			return []protocol318.InlineCompletionItem{
				{
					InsertText: "hello world",
					Range: &protocol316.Range{
						Start: protocol316.Position{
							Line:      0,
							Character: 0,
						},
						End: protocol316.Position{
							Line:      0,
							Character: 0,
						},
					},
				},
			}, nil
		},
		Handler: protocol317.Handler{
			Handler: protocol316.Handler{
				Initialized: initialized,
				Shutdown:    shutdown,
				SetTrace:    setTrace,
			},
		},
	}

	server := server.NewServer(&handler, lsName, false)

	server.RunStdio()
}

func initialize(context *glsp.Context, params *protocol318.InitializeParams) (any, error) {
	capabilities := handler.CreateServerCapabilities()

	return protocol318.InitializeResult{
		Capabilities: capabilities,
		ServerInfo: &protocol316.InitializeResultServerInfo{
			Name:    lsName,
			Version: &version,
		},
	}, nil
}

func initialized(context *glsp.Context, params *protocol316.InitializedParams) error {
	return nil
}

func shutdown(context *glsp.Context) error {
	protocol316.SetTraceValue(protocol316.TraceValueOff)
	return nil
}

func setTrace(context *glsp.Context, params *protocol316.SetTraceParams) error {
	protocol316.SetTraceValue(params.Value)
	return nil
}