fix(eslint-plugin): avoid-mapping-selectors don't report on ThisExpression

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #3511

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This scans if this is used in an operator.
If it finds a this, then the avoid-mapping-selectors rule is disabled.
The reasoning behind this, is that the selector is used in combination with something from the component (which can't be moved into the selector) to do something.

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