[Salsa] Support jsdoc `@namespace`

Support treating variable declarations with @namespace JSDoc tag as TS namespaces.

/** @namespace */
var Documents = {
    /**
     * An ordinary newspaper.
     */
    Newspaper: 1,
    /**
     * My diary.
     * @private
     */
    Diary: 2
};

[mhegazy]

you can just use:

// @filename: usage.js

/** @typedef {import('./interfaces').Foo} Foo */

/** @type {Foo} */
let foo;

[callionica]

Just here to say that I expected the following to work in a Javascript file and it didn’t work:

/** @namespace {import("vscode")} vscode */

/** @type {vscode.TextDocument} */

as a not very obvious workaround, I used

/** @type {import("vscode").TextDocument} */

instead.

It would be good if the first version using @namespace worked.