composer.json - Relax psr/log constraint. Improve D8 compatibility.

composer.json - Relax psr/log constraint. Improve D8 compatibility.

Overview
--------

This addresses a composer conflict that's reported when trying to install
on Drupal 8.7. For example, run these commands:

```
drush8 dl drupal-8.7.x
cd drupal-8*
composer require civicrm/civicrm-core:5.22.x-dev
```

This is a port of #16470 for `master`.

Before
------

The install fails because `civicrm-core` requires `psr/log:~1.1`, and something else
is prodding us to use `psr/log:1.0.2`.

```
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for civicrm/civicrm-core 5.22.x-dev -> satisfiable by civicrm/civicrm-core[5.22.x-dev].
    - Conclusion: remove psr/log 1.0.2
    - Conclusion: don't install psr/log 1.0.2
    - civicrm/civicrm-core 5.22.x-dev requires psr/log ~1.1 -> satisfiable by psr/log[1.1.0, 1.1.1, 1.1.2, 1.1.x-dev].
    - Can only install one of: psr/log[1.1.0, 1.0.2].
    - Can only install one of: psr/log[1.1.1, 1.0.2].
    - Can only install one of: psr/log[1.1.2, 1.0.2].
    - Can only install one of: psr/log[1.1.x-dev, 1.0.2].
    - Installation request for psr/log (locked at 1.0.2) -> satisfiable by psr/log[1.0.2].

Installation failed, reverting ./composer.json to its original content.
```

After
-----

It should work.  However, this is hard to demonstrate via `r-run` without merging.

Comments
--------

The substantive differences between `psr/log` in v1.0 and v1.1 relate to `LoggerInterfaceTest` and `TestLogger`:

https://github.com/php-fig/log/compare/1.0.2...1.1.2

However, `civicrm-core` does not use `LoggerInterfaceTest` or `TestLogger`, so it shouldn't matter.

For the standard tarballs which use `composer.lock`, this does have the side-effect of bumping up from 1.1.0 to 1.1.2.