Unity: added snippets for `sfield` and `requirecomponent`

[ThatAmuzak]

Sourced from https://github.com/kleber-swf/vscode-unity-code-snippets/blob/develop/snippets/snippets.json

These are new snippets that have been added since the last time this repository was used as a source (https://github.com/rafamadriz/friendly-snippets/commit/6ba7ee6ce4371e142fc9d7653020cb468932ec57)