not possible to un-ignore a file after ignoring through `should_ignore`

[TerminalFi]

Previously, LSP-Copilot had an open issue for how do we prevent a View/File from being managed by Github Copilot with disabling it on the entire syntax.

@jwortmann was kind enough to think this through and add the below function.

https://github.com/sublimelsp/LSP/blob/293f4a4340cca5ab1ad065643e4f20d9b270b2b1/plugin/core/sessions.py#L956-L965

However, now when we want to ignore a file, if that file is to ever be add back to the session, it requires asking the user to close and re-open the file or doing the below hack.

https://github.com/TerminalFi/LSP-copilot/blob/095fd059d1c6f7faaaedc75dc828ed83476d29f1/plugin/listeners.py#L61-L69

What this leads to is impacting other LSP sessions / plugins. See https://discord.com/channels/280102180189634562/1261340378133434439/1261340581779603497 for more details

Suggestion

Add another class func that can be used to trigger a view to be added to the LSP-* session