Fixes#15528
What is the current behavior?
The language service access TypeScript's Symbol.members without checking for null or undefined.
What is the new behavior?
The access is guarded.
This processor will eventually replace the `{@example}` inline tags
because it provides a cleaner approach that also supports tabbed examples
straight out of the box.
The idea is that authors will simply add a `path` and (optionally) a `region`
attribute to `<code-example>` or `<code-pane>` elements in their docs.
This indicates to dgeni that the relevant example needs to be injected
into the content of this element.
For example, assume that there is an example file `toh-pt1/index.hml` with
a region called `title`, which looks like:
```
<h1>Tour of Heroes</h1>
```
Then the document author could get this to appear in the docs as a
standalone example:
```
<code-example path="toh-pt1" region="title"></code-example>
```
Or as part of a tabbed group:
```
<code-tabs>
<code-pane path="toh-pt1" region="title"></code-pane>
</code-tabs>
```
If no `path` attribute is provided then the element is ignored, which
enables authors to provide inline code instead:
```
<code-example>
Some <html> escaped code
</code-example>
```
Also all attributes other than `path` and `region` are ignored and passed
through to the final rendered output allowing the author to provide
styling hints:
```
<code-example path="toh-pt1" region="title" linenums"15" class="important">
</code-example>
```
Fixes#14417
Updated example to illustrate @ContentChildren default behavior (only query direct children), and how to query for nested elements/all descendants.
This has the side effect of allowing `@Input` and `@ContentChild`
on the same property if the query is static (see the bug description
for details).
Fixes#15417
