Fix Viewer API definitions and include in CI

The Viewer API definitions do not compile because of missing imports and
anonymous objects are typed as `Object`. These issues were not caught
during CI because the test project was not compiling anything from the
Viewer API.

As an example of the first problem:

```
/**
 * @implements MyInterface
 */
export class MyClass {
    ...
}
```

will generate a broken definition that doesn’t import MyInterface:

```
/**
 * @implements MyInterface
 */
export class MyClass implements MyInterface {
    ...
}
```

This can be fixed by adding a typedef jsdoc to specify the import:

```
/** @typedef {import("./otherFile").MyInterface} MyInterface */
```

See https://github.com/jsdoc/jsdoc/issues/1537 and
https://github.com/microsoft/TypeScript/issues/22160 for more details.

As an example of the second problem:

```
/**
 * Gets the size of the specified page, converted from PDF units to inches.
 * @param {Object} An Object containing the properties: {Array} `view`,
 *   {number} `userUnit`, and {number} `rotate`.
 */
function getPageSizeInches({ view, userUnit, rotate }) {
    ...
}
```

generates the broken definition:

```
function getPageSizeInches({ view, userUnit, rotate }: Object) {
    ...
}
```

The jsdoc should specify the type of each nested property:

```
/**
 * Gets the size of the specified page, converted from PDF units to inches.
 * @param {Object} options An object containing the properties: {Array} `view`,
 *   {number} `userUnit`, and {number} `rotate`.
 * @param {number[]} options.view
 * @param {number} options.userUnit
 * @param {number} options.rotate
 */
```

web/ui_utils.js

@@ -284,12 +284,23 @@ function roundToDivide(x, div) {
   return r === 0 ? x : Math.round(x - r + div);
 }
 
+/**
+ * @typedef {Object} GetPageSizeInchesParameters
+ * @property {number[]} view
+ * @property {number} userUnit
+ * @property {number} rotate
+ */
+
+/**
+ * @typedef {Object} PageSize
+ * @property {number} width - In inches.
+ * @property {number} height - In inches.
+ */
+
 /**
  * Gets the size of the specified page, converted from PDF units to inches.
- * @param {Object} An Object containing the properties: {Array} `view`,
- *   {number} `userUnit`, and {number} `rotate`.
- * @returns {Object} An Object containing the properties: {number} `width`
- *   and {number} `height`, given in inches.
+ * @param {GetPageSizeInchesParameters} params
+ * @returns {PageSize}
  */
 function getPageSizeInches({ view, userUnit, rotate }) {
   const [x1, y1, x2, y2] = view;