[llvm] [DAG] Add generic m_TernaryOp() / m_c_TernaryOp() matchers (PR #165520)

[Hongyu Chen via llvm-commits]

https://github.com/XChy commented:

Looks like most code in visitFMA can be replaced with SDPatternMatch helpers.

https://github.com/llvm/llvm-project/pull/165520