Threaded client message reader

[oisanjaya]

I am trying to enable CheckSyntax in TDidChangeTextDocument.Process() like Michael do, but the problem is RunMessageLoop() read stdio synchronously so when we type into a file rapidly "asdf", for example, here's what currently happen:

• client sent textDocument/didChange (identifier "a")
• pasls read input buffer
• CheckSyntax() run (take a long time)
• before CheckSyntax() return client already sent textDocument/didChange (identifier "as"), pasls still busy, not read
• before CheckSyntax() return client already sent textDocument/didChange (identifier "asd"), pasls still busy, not read
• before CheckSyntax() return client already sent textDocument/didChange (identifier "asdf"), pasls still busy, not read
• CheckSyntax() return with 'unknown identifer: "a"'
• pasls read input buffer textDocument/didChange (identifier "as")
• CheckSyntax() run (take a long time)
• CheckSyntax() return with 'unknown identifer: "as"'
• pasls read input buffer textDocument/didChange (identifier "asd")
• ...and so on

For larger codebase like Lazarus current mechanism effectively hangs pasls.

This PR factor out task of reading stdio into separate thread. That thread queue incoming message into shared TJSONSignaledQueue. RunMessageLoop() in main thread wait for shared TJSONSignaledQueue to be ready to read.

Shared RequestQueue: TJSONSignaledQueue also debounced textDocument/didChange notification message that only last notification in queue will be consumed by pasls, hence only run CheckSyntax on latest change.