Map key order

[gorkem]

What does this PR do?

Introduces a new setting yaml.keyOrder that enforces the alphabetical key order for mappings when set to true.
In addition to validation, it also provides a code action to fix the order for the map

What issues does this PR fix or reference?

redhat-developer/vscode-yaml#95

Is it tested? How?

Adds tests for validation, new settings and code action

[coveralls]

Coverage: 83.05% (-0.05%) from 83.103% when pulling 37505b4 on gorkem:map-key-order into 64e3815 on redhat-developer:main.

[msivasubramaniaan]

LGTM

[polyzen]

Seems this should be false.

[snaggen]

When I open a yaml file now in neovim (where I have installed yamlls via Mason and default config) I get a lot of "Wrong order of key" in my docker-compose.yaml and .gitlab-ci.yml files. I have tried to disable it by setting keyOrdering = false but with no improvement.
Also, when looking at https://github.com/neovim/nvim-lspconfig/blob/master/lua/lspconfig/server_configurations/yamlls.lua it sems that they are not enabling this in their default config.

Edit:
Setting this att the latest possible stage seems to fix the neovim issue, since I use mazon-lspconfig it didn't work to set this in the lspconfig, but when I set it in mason-lspconfig it worked. Here is the mason-lspconfig I use with Lazy, just for anywone with the same issue.

 {
        "williamboman/mason-lspconfig.nvim",
        config = function(_, opts)
            require("mason-lspconfig").setup_handlers {
                function(server_name)
                    require("lspconfig")[server_name].setup {}
                end,
                ["yamlls"] = function()
                    require("lspconfig").yamlls.setup({
                        settings = {
                            yaml = {
                                keyOrdering = false
                            }
                        }
                    })
                end
            }
        end
    },