Proportional, granular progress updates for installing

[HebaruSan]

Motivation

• There are no UI updates while a mod is being installed, which can take a long time for a very large mod and may make it look like the GUI is frozen
• The progress bar for installing mods treats tiny mods and huge mods as an equal percentage of the install, which makes it useless for estimating how complete the install actually is
• The mod installation progress bar counts up from 0% to 60% for the actual unzipping, and then the remaining 40% reflects saving the registry (which became a lot faster in Refactor repository and available module handling #3904) and completing the transaction (which is basically instantaneous), which likewise makes the progress bar less reflective of overall completion

Changes

• Now we generate at least one progress update per file being unzipped, and another progress update every 200 milliseconds after that for large files, so large mods will have many gradual updates to the progress bar, and you'll be able to tell that it's still installing
• Now installation progress updates are scaled proportionally to the number of bytes installed, so the progress bar will reflect how far along you are in the overall install
• Now mod installation is given 85% of the progress bar, with saving the registry and finishing the transaction relegated to the remaining 15%

Fixes #4014.

Side fixes

• The timer from Trigger progress updates for frozen downloads #4052 was continuing to run and generate spurious updates after downloads completed. Now it's properly destroyed.
• ModuleInstaller.onReportModInstalled is now a proper event, and its type is Action<CkanModule> instead of a custom delegate
• ModuleInstaller.InstallModule formerly returned IEnumerable<string>, which isn't a great idea for a collection that's going to be passed to other functions because IEnumerable<> often involves lazy evaluation, which may cause performance problems if evaluated multiple times. Now it's a List<string>.
• ModuleInstaller.ksp is renamed to instance