Fix dead links

[sdirix]

• https://apidevtools.org/json-schema-ref-parser/docs/plugins/resolvers.html linked from https://jsonforms.io/docs/deprecated/ref-resolving-legacy/
• https://github.com/eclipsesource/jsonforms/blob/master/packages/vanilla/Styles.md linked from https://jsonforms.io/api/vanilla/index.html
• https://jsonforms.io/api/vue/vue/README.md linked from https://jsonforms.io/api/vue/vue-vanilla/index.html
• https://jsonforms.io/api/vue/vue-vanilla/src/styles/defaultStyles.ts linked from https://jsonforms.io/api/vue/vue-vanilla/index.html
• https://jsonforms.io/api/vue2/vue2/README.md linked from https://jsonforms.io/api/vue2/vue2-vanilla/index.html
• https://jsonforms.io/api/vue2/vue2-vanilla/src/styles/defaultStyles.ts linked from https://jsonforms.io/api/vue2/vue2-vanilla/index.html

For the API links: Also fix the link in the source files to avoid them being generated and copied over with the next release.