• fileExists and readFile of the CompilerHost created by Language service created script infos but it shouldn't because the getSourceFile is the correct api to get those since the script infos (scriptsnapshot and watcher for the file) are always associated to the project they are requested from. The issue here was that the script infos created by fileExists and readFile would get the project assigned but never removed because they weren't part of project's source file. 1bf1209 fixes this by directing those call to host instead.
• When project is removed it removed the script shot of open file/s from that project but it never use to remove it for files are not open. For big projects that meant huge strings and rest of the stuff still in memory. 2ec92b9 cleans up the ScriptInfos not associated with any project to reduce footprint left behind by closing files. This change also cleans up few pointers to make sure project, LShost, LS and other structures that are related to the project are cleaned up
• 98cb0ce moves the cleanup of orphan script infos to after next open file so that we can reuse the script infos if the file from the previously closed project is opened right after that.

Fixes microsoft/vscode#28112 and #16329