Unclosed element tags are not assigned an `endSourceSpan` by the parser.
As a result, the visitor which determines the target node at a position
for the language service was unable to determine that a given position
was inside an unclosed parent. This happens because we update the
`endSourceSpan` of template/element nodes to be the end tag (and there
is not one for unclosed tags). Consequently, the visitor then cannot
match a position to any child node location.
This change updates the visitor logic to check if there are any
`children` of a template/element node and updates the end span to be the
end span of the last child. This allows our `isWithin` logic to identify
that a child position is within the unclosed parent.
Addresses one of the issues found during investigation of https://github.com/angular/vscode-ng-language-service/issues/1399
PR Close#42554
228beeabd1