Move single pre-process proposal file to the new location.

### Motivation:

To have all the proposals in one place.

### Modifications:

One .md file moved.

### Result:

All proposals are in one place.

Co-authored-by: Konrad `ktoso` Malawski <konrad_malawski@apple.com>

Make InMemoryLogging available on all platforms

### Motivation:

Users might want to adopt the in memory logger on lower platform
versions.

### Modifications:

Remove availability annotations by using swift-logs own Lock instead of
Mutex

### Result:

In memory logger can be used on all platforms that swift-log supports