Maven support should check for toolchains.xml

### Description

Toolchains may be used by a project; in case of e.g. apache Cocoon, if there's no toolchains definition, the project compilation fails.
NB IDE could check for user toolchains.xml file and if missing provide its own generated on-the-fly based on JDK that NB executes on. This would not affect user machine setup and only activate in cases the user does not define any tools.

NB IDE could also attempt to synchronize its configured Java platforms with the user toolchains.xml

### Use case/motivation

This feature would allow to compile more projects 'out of the box' on a clean machine. Manipulating with platforms would also configure machine's Maven build environment.

### Related issues

#5978

### Are you willing to submit a pull request?

Yes

The issue names NetBeans Maven support and user toolchains.xml, with related issue #5978. Start by locating the Maven support entry points and existing Java platform configuration; determine how missing user toolchains are detected and how configured platforms could be synchronized. Done should cover clean-machine compilation when no user toolchain is defined without altering existing machine setup.

Written by the indexing model from the issue text.