search-in-workspace: add support for multi-line searches

[vince-fugnitto]

Feature Description:

The goal is to add support for multi-line searches in the search-in-workspace view. The changes likely include:

• updating the input to a textarea
• passing the proper options to ripgrep

vscode above - theia below:

How to test:

1. search the following in the search-in-workspace view:

export const GettingStartedCommand = {
    id: GettingStartedWidget.ID,
    label: GettingStartedWidget.LABEL
};