Add code bundling with webpack

[evidolob]

What does this PR do?

This PR based on #591 @fbricon work.
It just add bundling of yaml-ls in languageserver.js file.

Note: I keep prettier unbundled as it contains quite big and already bundled files.

For me vscode shows 78ms activation time with this PR, comparing to 303ms for 0.22.0 version
And vsix file now contains 50 files, 4.23MB size, comparing to 1829 files, 8.5MB for 0.22.0.

The only thing that we may loose that error stack traces now doesn't contains any readable names, so it would be hard to find problem if user/telemetry report any trace.

What issues does this PR fix or reference?

#521

Is it tested? How?

[fbricon]

Can we trim some prettier fat? You should just need parser-yaml

[evidolob]

@fbricon I include in vsix package only needed prettier files, now package contains 20 files, 840.42KB
But we need to double check that everything works well

[gorkem]

I have built and tested briefly, no problems and seems like an improvement.