Move non-main solutions to src/ subdir #2566

Job	Run time
macOS--dotnet6-only	5m 48s
macOS--dotnet6-only	5m 48s
macOS--mono-only	15m 10s
macOS--mono-only	15m 10s
macOS--dotnet6-and-mono	6m 50s
macOS--dotnet6-and-mono	6m 50s
linux22-github--dotnet-and-mono	4m 46s
linux22-github--dotnet-and-mono	4m 46s
linux22-github--dotnet-and-newmono	4m 10s
linux22-github--dotnet-and-newmono	4m 10s
windows--dotnet6-and-legacyFramework	9m 15s
windows--dotnet6-and-legacyFramework	9m 15s
windows--dotnet6-only	7m 49s
windows--dotnet6-only	7m 49s
windows--legacyFramework-only	13m 57s
windows--legacyFramework-only	13m 57s
linux22-vanilla--stockdotnet6-and-newmono	6m 25s
linux22-vanilla--stockdotnet6-and-newmono	6m 25s
linux22-vanilla--stockdotnet6-and-stockmono	5m 46s
linux22-vanilla--stockdotnet6-and-stockmono	5m 46s
linux22-vanilla--stockdotnet6-only	5m 31s
linux22-vanilla--stockdotnet6-only	5m 31s
linux22-vanilla--stockmono-only	5m 54s
linux22-vanilla--stockmono-only	5m 54s
linux20-github--dotnet-and-mono	3m 42s
linux20-github--dotnet-and-mono	3m 42s
linux20-vanilla--newmono-only	10m 48s
linux20-vanilla--newmono-only	10m 48s
linux20-github--dotnet-and-newmono	5m 50s
linux20-github--dotnet-and-newmono	5m 50s
linux20-vanilla--stockmono-only	1m 54s
linux20-vanilla--stockmono-only	6m 54s
linux22-vanilla--newmono-only	12m 16s
linux22-vanilla--newmono-only	12m 16s
conventions	0s
conventions	1m 38s
snap_pkg	0s
snap_pkg	12m 49s
	4h 31m 9s

Provide feedback