[MLA-1824] make SensorComponent return ISensor[]

[chriselion]

Proposed change(s)

• Changes SensorComponent to return an array of sensors instead of just 1.
• Update Match3 sensors to only operate on one of cell values or special values at a time. Match3SensorComponent will return a sensor for cell values, and another for special values (if there are any). Note that this invalidates previously trained models.

Note that Match3 models were only retrained partially, since I expect them to change again soon.

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

https://jira.unity3d.com/browse/MLA-1824

Types of change(s)

• Code refactor
• Breaking change

Checklist

• Added tests that prove my fix is effective or that my feature works
• Updated the changelog (if applicable)
• Updated the migration guide (if applicable)

Other comments

[chriselion]

Disabled for now, might return later (depending on how I handle multiple board sizes)

[surfnerd]

does this loop exist to 0 out the rest of one-hots? Could it be simplified to something like:

writer[offset + val] = 1.0f;

[chriselion]

Yeah, as long as we know the memory is initialized to zero, we could do that (plus an extra check that val < m_OneHotSize)

[surfnerd]

LGTM