Add Handlebars.parseWithoutProcessing (#1584)

When authoring tooling that parses Handlebars files and emits Handlebars
files, you often want to preserve the **exact** formatting of the input.
The changes in this commit add a new method to the `Handlebars`
namespace: `parseWithoutProcessing`. Unlike, `Handlebars.parse` (which
will mutate the parsed AST to apply whitespace control) this method will
parse the template and return it directly (**without** processing
😉).

For example, parsing the following template:

```hbs
 {{#foo}}
   {{~bar~}} {{baz~}}
 {{/foo}}
```

Using `Handlebars.parse`, the AST returned would have truncated the
following whitespace:

* The whitespace prior to the `{{#foo}}`
* The newline following `{{#foo}}`
* The leading whitespace before `{{~bar~}}`
* The whitespace between `{{~bar~}}` and `{{baz~}}`
* The newline after `{{baz~}}`
* The whitespace prior to the `{{/foo}}`

When `Handlebars.parse` is used from  `Handlebars.precompile` or
`Handlebars.compile`, this whitespace stripping is **very** important
(these behaviors are intentional, and generally lead to better rendered
output).

When the same template is parsed with
`Handlebars.parseWithoutProcessing` none of those modifications to the
AST are made. This enables "codemod tooling" (e.g. `prettier` and
`ember-template-recast`) to preserve the **exact** initial formatting.
Prior to these changes, those tools would have to _manually_ reconstruct
the whitespace that is lost prior to emitting source.

types/test.ts

@@ -192,4 +192,12 @@ switch(allthings.type) {
     break;
   default:
     break;
-}
+}
+
+function testParseWithoutProcessing() {
+  const parsedTemplate: hbs.AST.Program = Handlebars.parseWithoutProcessing('<p>Hello, my name is {{name}}.</p>', {
+    srcName: "/foo/bar/baz.hbs",
+  });
+
+  const parsedTemplateWithoutOptions: hbs.AST.Program = Handlebars.parseWithoutProcessing('<p>Hello, my name is {{name}}.</p>');
+}