Add initial syntax

[rchl]

Add syntax for ESPHome configuration files.

This syntax extends YAML syntax to add support for lambda key/tag that can embed c++ code blocks.

Something to consider:

I've chosen a source.yaml-esphome main scope instead of source.yaml.esphome mainly due to how LSP works but also to match the vscode syntax.

The advantage of source.yaml-esphome in context of LSP is that the YAML language server will NOT automatically run for this syntax and we don't want that since it doesn't understand extensions of this syntax. Alternatively we could use source.yaml.esphome and edit LSP-yaml's configuration to exclude it.

One disadvantage of source.yaml-esphome that I've noticed is that built-in color schemes (f.ex. Mariana) include a rule to color unquoted strings white and that won't automatically work with source.yaml-esphome scope. There are perhaps also other YAML packages/plugins that would not automatically work with that scope.

[rchl]

Thanks for awesome suggestions.

[rchl]

Also noticed that return here is not colored for example:

but that is probably an issue in the c++ syntax since it's reproducible also in c++ syntax with leading spaces:

[deathaxe]

This is somehow related with how, c++ syntax handles global scopes.

If - as it seems - normal statements are required, only, it may be viable to include source.c++#statements context only, which would fix this kind of issues.

[rchl]

This seems to produce better highlighting all around so I will go with that. Thanks!