Language client configuration provider feature

[angelozerr]

This PR provides a new attribute for languageServer extension point called languageClientConfigurationProvider

Here a sample with CSS:

<extension
         point="org.eclipse.lsp4e.languageServer">
      <server
            class="org.eclipse.wildwebdeveloper.css.CSSLanguageServer"
            languageClientConfigurationProvider="org.eclipse.wildwebdeveloper.css.CSSLanguageClientConfigurationProvider"
           ...>

This languageClientConfigurationProvider expects an implementation of LanguageClientConfigurationProvider which looks like this:

package org.eclipse.lsp4e;

import java.util.List;
import java.util.concurrent.CompletableFuture;

import org.eclipse.lsp4j.ConfigurationParams;
import org.eclipse.lsp4j.FormattingOptions;
import org.eclipse.lsp4j.TextDocumentIdentifier;

public interface LanguageClientConfigurationProvider {

	CompletableFuture<List<Object>> configuration(ConfigurationParams configurationParams);

	default void collectFormatting(FormattingOptions formattingOptions, TextDocumentIdentifier identifier, String languageId) {
		// Do nothing
	}
}

This API gives the capability to:

• defines client configuration (instead of implementing LanguageClientImpl)
• collect special formatting options that the language server could require to format like the CSS language server.

[angelozerr]

See sample with CSS language server eclipse-wildwebdeveloper/wildwebdeveloper#962

[mickaelistria]

The initial target branch master was deleted and replaced by main, so this PR got closed automatically. If this is still relevant, please re-create this PR targetting the main branch.