Update codegen to use `Node.JS` where applicable

[maorleger]

This is a follow-up to https://github.com/Azure/azure-sdk-for-js/issues/21038

For example: https://github.com/Azure/autorest.typescript/blob/766e65635070a5aea404b210334bbf50bb85cb81/src/generators/modelsGenerator.ts#L322

Should instead be consistent with the rest of the docs by using "ONLY AVAILABLE IN NODE.JS RUNTIME"

For browser-only, we should use "ONLY AVAILABLE IN BROWSERS"

Finally, anywhere we generate "node", "Node", "nodejs", etc. we should instead use "Node.JS"

cc @diberry