v0.22.0

Update to AssemblyScript version 0.19.10.

This version breaks compatibility with older versions of graph-ts.

Main changes were:

• Some ethereum classes have constructors now.
• Added new static methods for constructing zero and/or empty values for:
  • Address
  • BigInt
  • BigDecimal
  • ByteArray
  • Bytes
• Addition of assertions to arithmetic operator overloaders in the case of the left hand side of the operation being nullable.
• Renaming of ethereum's transaction field gasUsed to gasLimit. This field has always been filled with the value of the gasLimit, now the name is correct. To follow up on the support for gasUsed, look: graphprotocol/graph-node#2619.