Masquerade URL token

Problem/Motivation

Masquerade link is dynamically generated. Currently, there is only a link at the user profile page. There is a feature request to add such link in views result (#3060679: Views field to masquerade as), but there are some other contexts where a masquerade to user link could be required. Having the masquerade link available as a token would be useful in those scenarios.

Steps to reproduce

N/A

Proposed resolution

Add a masquerade URL token in the user token group.

Remaining tasks

Review, tests.

User interface changes

None.

API changes

None.

Data model changes

N/A