[Docs] Merge with-mobx-state-tree with with-mobx-state-tree-typescript example

[HaNdTriX]

Changes

see commits

Context

As discussed in #40302 (comment) we are going to merge the mobx examples.

#40302

Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[balazsorban44]

Thanks!