[llvm] [TableGen] Extract InstructionEncoding class into a separate file (NFC) (PR #158505)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

The first commit moves `IgnoreNonDecodableOperands` check from `addOneOperandFields` to `emitBinaryParser`.
I could not declare the option as `extern` because `TableGenCommon` is built as shared library in some configurations.


https://github.com/llvm/llvm-project/pull/158505