Prepare 1.4.0 release

[dexcompiler]

Summary

• bump Clockworks package version to 1.4.0
• move accumulated changelog entries into a dated 1.4.0 section
• update changelog compare links for the next Unreleased range

Validation

• DOTNET_CLI_HOME=/tmp/clockworks-dotnet NUGET_HTTP_CACHE_PATH=/tmp/clockworks-nuget-http NUGET_PACKAGES=/tmp/clockworks-nuget-packages dotnet test Clockworks.sln -v minimal -m:1
• npm run docs:build
• DOTNET_CLI_HOME=/tmp/clockworks-dotnet NUGET_HTTP_CACHE_PATH=/tmp/clockworks-nuget-http NUGET_PACKAGES=/tmp/clockworks-nuget-packages dotnet pack src/Clockworks.csproj -c Release -v minimal

Release note

Pack validation produced src/bin/Release/Clockworks.1.4.0.nupkg locally.