Do not load Path call receiver if known to be pure load

[HertzDevil]

Follow-up to #15485.

The compiler always emits LLVM instructions to load the receiver of a call even if it has a metaclass type, because there could be other side effects. This adds a large number of superfluous type ID loads when calling class methods:

  %0 = load i32, ptr @"Foo0.class:type_id", align 4
  %1 = call ptr @"*Foo0@Reference::new:Foo0"()
  %2 = load i32, ptr @"Foo1.class:type_id", align 4
  %3 = call ptr @"*Foo1@Reference::new:Foo1"()
  %4 = load i32, ptr @"Foo2.class:type_id", align 4
  %5 = call ptr @"*Foo2@Reference::new:Foo2"()
  ; ...

Although .new does load the type ID later, this ID should never show up as an implicit argument to the Foo*.new methods. Here the %0, %2, and %4 variables are a consequence of un-inlining the type IDs. This PR removes those loads when the call receiver is a Path known to refer to a non-generic metaclass type. (In isolation, the PR skips over whatever is in Crystal::CodeGenVisitor#visit(Crystal::Path).)