Support full fidelity YAML round-tripping

[lblackstone]

This change uses the new YAML parsing library to
to implement full fidelity round-tripping of config files.
Any comments and formatting will now be preserved
when Pulumi writes changes to disk.

Fix #423
Fix #6480
Fix #5235

TODO:

• Swap out YAML package
• Add logic to marshal/unmarshal YAML to AST
• Update config set/rm to use AST
• Add tests
• Update config setAll/rmAll to use AST
• Update Project and PolicyPackProject round-tripping (Going to follow up with this later)
• Support structured config set/rm

[squaremo]

Rebasing this looks tractable -- is it worth bringing it up to date, @lblackstone? I can review it.

[lblackstone]

Rebasing this looks tractable -- is it worth bringing it up to date, @lblackstone? I can review it.

Check out this comment about the state I left this in. The following comments in that thread also make me question whether the current duality of using the config as both user-editable as well as Pulumi-editable actually makes sense. I'll defer to @pulumi/platform on the latter question.

[AaronFriel]

@Frassle I think this looks like a good candidate to pull in to this or the next iteration as we're considering adding another place where we mutate the stack config: seeding names.

[Frassle]

The following comments in that thread also make me question whether the current duality of using the config as both user-editable as well as Pulumi-editable actually makes sense. I'll defer to

I don't think we're going to get away from that. If anything its going to get worse with ideas around yaml programs wanting to modify the Pulumi.yaml not just the Pulumi.<stack>.yaml.

@Frassle I think this looks like a good candidate to pull in to this or the next iteration as we're considering adding another place where we mutate the stack config: seeding names.

Yeh if this is close to done and doesn't have any major issues it would be good to get finished.

[AaronFriel]

Implemented in #11456