Form example

[philip-peterson]

Description

Provides a form example with a controlled input and a component that manages the state.

Checklist:

• I have run ./ci/run_stable_checks.sh
• I have reviewed my own code
• I have added tests

[siku2]

We have a big number of examples already so I'm currently trying to organize and structure them a bit better.
In fact, there are so many examples that I honestly don't have a solid grasp for what they demonstrate.
Given that, let me raise the question: Does this warrant its own example or could we perhaps extend one of the existing examples to include this?

If you feel like this deserves its own example then there are some things that I would like to have added:

We have a little table in examples/README.md giving an overview of all examples. Please update it accordingly.
Notice how there's a "has readme" column, that's because I feel like all examples should have a README.md further outlining their purpose.

The README.md should contain the following:

• A detailed description of what the example demonstrates
• A table containing the following details:
  • Yew version the example was originally written in
  • author of the example

I know most examples are currently a bit of a free-for-all but I think it's necessary to start organizing them better going forward.
Not only to ease the maintenance burden but also to make it easier for users to learn something from them.

Since this is the first example you're free to set a precedent here.