Make sure last LSP client is disconnected before creating a new one.

[jstraceski]

The LSP client seems to have left over resources when restarting godot.
This causes CTRL-hover to fail after restarting godot because multiple textDocument/definition requests are sent.

Steps to reproduce issue:

1. Open vscode extension.
2. Open godot project.
3. Within the vscode window CTRL-Click any object.
4. Close + reopen godot.
5. Within the vscode window CTRL-Click any object.

If you have a debuging window open you should see rx/tx similar to this:

[lsp.io] tx: {jsonrpc: '2.0', id: 4, method: 'textDocument/hover', params: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', id: 22, method: 'textDocument/hover', params: {…}}
logger.ts:70
[lsp.io] rx: {id: 4, jsonrpc: '2.0', result: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', method: '$/cancelRequest', params: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', id: 5, method: 'textDocument/definition', params: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', id: 23, method: 'textDocument/definition', params: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', id: 6, method: 'textDocument/hover', params: {…}}
logger.ts:70
[lsp.io] tx: {jsonrpc: '2.0', method: '$/cancelRequest', params: {…}}
logger.ts:70

This change disconnects io functions, and stops the last valid LSP client before making a new client.

(I did test this on godot > 4.5 but I have made some local changes so there is a chance that it is not required under the current stable godot version.)

[HolonProduction]

Could you check whether your original issue was solved by #968

This PR looks alright as safeguard. But in concept create_new_client should only be called when the old client is in a state were it is disconnected and will never reconnect.

[Nallebeorn]

I tested a build of this branch, and it seems to fix #978. At least with the repro steps of restarting Godot that are described in the comments.

[Calinou]

@HolonProduction Do you think this is safe to merge? If so, I can merge it and tag 2.6.2.

[HolonProduction]

The client?.stop part makes sense to me. While client client.io is public, it really should be a private member and cleaning it up at this place breaks encapsulation to me.

I verified that just the client?.stop part fixes #978 it probably contains some code to unregister the client with VSCode.