Add support for package:web v1.0.0 (#3821)

Add support for package:web v1.0.0

- Expands version range to >=0.5.1 <2.0.0.
- In order to do this, we add an `innerHtml` extension
interop member both so we can support both major
versions and so we don't need to do manual conversions
of JSAny.
- Also updates `createElement` calls to use the constructors
supplied in package:web 0.5.1 onwards.

Author: srujzs

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 8.0.12
 
- * Allow `markdown-alert` class names in HTML sanitization. (#3820)
+* Allow `markdown-alert` class names in HTML sanitization. (#3820)
+* Require package `web: '>=0.5.1 <2.0.0'`.
 
 ## 8.0.11