Update license descriptions also in POMs and headers

[ftomassetti]

As a follow up of #144 we should update the license description also in:

• POMs (see buildSrc/src/main/kotlin/com/strumenta/antlrkotlin/gradle/ext/MavenPublishBaseExtension.ext.kt)
• The runtime sources (see antlr-kotlin-runtime/src/jsAndWasmSharedMain/kotlin/com/strumenta/antlrkotlin/runtime/WeakHashMap.kt, for example)

[lppedd]

@ftomassetti for the runtime sources, we can use a very simple message, like this.

It's not required to re-write the entire license(s) for every source file.

[ftomassetti]

@ftomassetti for the runtime sources, we can use a very simple message, like this.

Agreed

[lppedd]

Agreed

Sounds good. Let me know if you want me to replace all headers while you change the publishing related stuff.
We just need to agree on what the header should look like, maybe:

// Copyright 2017-2024 Strumenta and contributors, licensed under Apache 2.0.
// Copyright 2024 Strumenta and contributors, licensed under BSD 3-Clause.

The above covers both the licenses, and states for which years the license is valid. That's all it should take. I've checked what we do here and legal says per-file copyright is not a requirement, so it can just briefly describe the license types.