Defer InlineCompletionsModel to after the editor has opened

[Tyriar]

Currently InlineCompletionsModel is initialized in the microtasks of the mousedown even when opening an editor. This add 7ms at least to the opening that seems like it could easily be avoided. This may not seem like much but it can also contribute to GC pressure and we're suffering right now from so many things happening when an editor opens that it's causes a very noticeable delay when switch editors.

Repro:

1. Open 2 big files (not sure how important big it, I was using terminalInstance.ts and runInTerminalTool.ts)
2. Start a trace
3. Switch between them
4. End trace

[Tyriar]

This also seems related: