fix: increase walker queue buffer & start walking early

[radeksimko]

This was introduced as part of #502 (i.e. the bug thankfully isn't part of a release)

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Due to limited channel buffer size, the walker queueing would be blocked on any 2nd path here:

terraform-ls/internal/langserver/handlers/initialize.go

Line 153 in cf0650f

walker.EnqueuePath(modPath)

or here

terraform-ls/internal/langserver/handlers/initialize.go

Line 190 in cf0650f

walker.EnqueuePath(fh.Dir())

and it would remain blocked forever as it would also block starting the walker and therefore consumption from the channel.

Attached test times out without the patch.

[github-actions]

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