Page.open() / Page.setLocation() functionality added

[Lozadaa]

fix to issue #4869

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This change is 

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[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[vaadin-bot]

Document the parameter(s): url

[vaadin-bot]

File contains tab characters (this is the first instance).

[vaadin-bot]

SonarQube analysis reported 5 issues

• 1 blocker
• 1 critical
• 3 major

Watch the comments in this conversation to review them.

3 extra issues

Note: The following issues were found on lines that were not modified in the pull request. Because these issues can't be reported as line comments, they are summarized here:

1. Page.java#L74: Call "Optional#isPresent()" before accessing the value.
2. Page.java#L88: Call "Optional#isPresent()" before accessing the value.
3. Page.java#L422: Define and throw a dedicated exception instead of using a generic one.