Port "Text comparison (text_matches)" condition to 8.x

Hi, I have published a first draft of this ticket implementation in the following PR: https://github.com/fago/rules/pull/106
It's not complete yet, but it represents a starting point for further discussions, as I have a few questions(see on the PR comment).

I am not sure of the status of this issue based on the discussion in the pull request, but here is a simple, direct port of the "Text comparison" condition from Drupal 7 (based on the existing D8 "Data Comparison" condition).

While I think we want to replace this functionality with #2681735: Add support for data matcher plugins, I think it's fine to complete this to have the functionality ported and working for now. Or do we want to avoid having this condition in the first place, so we do not have to keep supporting it during updates?

I didn't see any progress on the data matcher stuff so I think we should have a straight port of this functionality first. Let's worry about update path before beta.

Based on previous comments, setting to needs review.

I have a rule where on user login it runs a condition where it checks the current page path using this plugin and then fires a redirect action.

When I log in and it runs I get:

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "rules_text_comparison" plugin does not exist. in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 52 of core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).

Clearing the cache doesn't help.

It seems that error was somehow related to my doing a config import from development to staging.
I'm pretty sure I did a 'drupal cache:rebuild' before running the config import but it didn't seem to help.

After clearing the cache from the performance UI it all seems to work again.

A test case is missing and please file a pull request against https://github.com/fago/rules/pulls

I will write the test.

Here is a patch containing:

1. src/Plugin/Condition/TextComparision.php - the port from #8, with cleaned-up coding standards.
2. tests/src/Unit/Integration/Condition/TextComparisonTest.php - a new test with unit tests of this condition and all its options.

Removed the unused 'use' statement.

I didn't see any progress on the data matcher stuff so I think we should have a straight port of this functionality first. Let's worry about update path before beta.

oh yes, let's do not wait for this...

Patch is good and has test coverage.