fix(language-service): diagnostic and definition should work for absolute url

[kyliau]

This commit fixes a bug in the View Engine implementation of
getSemanticDiagnostics and getDefinitionAndBoundSpan for node in the
decorator metadata that represents an external URL
(templateUrl or styleUrls).

The URL could be either relative or absolute, but the latter was not taken
into account.

Fix angular/vscode-ng-language-service#1055

PR Checklist

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

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