feat: static variable analysis (#770)

* feat: static variable analysis

* Accept any iterable from `children`, `arguments`, etc.

* Test analysis of standard tags

* Use `TagToken.tokenizer` instead of creating a new one

* Test analysis of netsted tags

* Group variables by their root value

* Test analysis of nested globals and locals

* Analyze included and rendered templates WIP

* Use existing tokenizer when constructing `Hash`

* Improve test coverage

* Analyze variables from `layout` and `block` tags

* Test analysis of Jekyll style includes

* Handle variables that start with a nested variable

* Async analysis

* Test non-standard tag end to end

* Implement convenience analysis methods on the `Liquid` class

* More analysis convenience methods

* Accept string or template array

* Draft static analysis docs

* Deduplicate variables names

* Fix isolated scope global variable map

* Coerce variables to strings instead of extending String

* Private map instead of extending Map

* Fix e2e test

* Tentatively implement analysis of aliased variables

* Fix nested variable segments array

* Update docs sidebar

test/integration/util/error.spec.ts

@@ -264,7 +264,7 @@ describe('error', function () {
     it('should throw ParseError when tag value not specified', async function () {
       await expect(engine.parseAndRender('{% if %}{% endif %}')).rejects.toMatchObject({
         name: 'TokenizationError',
-        message: 'invalid value expression: "", line:1, col:1'
+        message: 'invalid value expression: "", line:1, col:6'
       })
     })
     it('should throw ParseError when tag parse throws', async function () {