- #3122 and #3123 (5 of 5)
- avoid concatenating values and wrapping them in an `HtmlString`
- switch from `string.Format()` to `AppendHtml()` in `LinkTagHelper`
- simplify `RazorPage` and `TagHelperContentExtensions` e.g. don't use a `TagHelperContentWrapperTextWriter`
- add some special cases in `UrlResolutionTagHelper`
- add `TagBuilder` and `StringHtmlContent` special cases to avoid `StringWriter` use when value is an `HtmlString`
- move `HtmlTextWriter` optimizations a bit lower and add missing checks for that type
nits:
- correct comments that incorrectly mention `HtmlString`s
- update comments in `JavaScriptStringArrayEncoder`
- wrong fix especially now that test encoders work as expected
- touch up `HtmlHelperTest` and `RazorViewTest` since test encoders are now consistent
- remove references to old `Microsoft.Extensions.WebEncoders.Testing` package
This reverts commit a9d5876cd9.
- but leave `FormTagHelperTest` and `ValidationMessageTagHelperTest` cleanup alone
nit: use `string.Empty` in `HtmlHelperLinkGenerationTest`