Rollup merge of #124797 - beetrees:primitive-float, r=davidtwco

Refactor float `Primitive`s to a separate `Float` type

Now there are 4 of them, it makes sense to refactor `F16`, `F32`, `F64` and `F128` out of `Primitive` and into a separate `Float` type (like integers already are). This allows patterns like `F16 | F32 | F64 | F128` to be simplified into `Float(_)`, and is consistent with `ty::FloatTy`.

As a side effect, this PR also makes the `Ty::primitive_size` method work with `f16` and `f128`.

Tracking issue: #116909

`@rustbot` label +F-f16_and_f128

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs

@@ -122,10 +122,7 @@ fn tag_base_type<'ll, 'tcx>(
             // Niche tags are always normalized to unsized integers of the correct size.
             match tag.primitive() {
                 Primitive::Int(t, _) => t,
-                Primitive::F16 => Integer::I16,
-                Primitive::F32 => Integer::I32,
-                Primitive::F64 => Integer::I64,
-                Primitive::F128 => Integer::I128,
+                Primitive::Float(f) => Integer::from_size(f.size()).unwrap(),
                 // FIXME(erikdesjardins): handle non-default addrspace ptr sizes
                 Primitive::Pointer(_) => {
                     // If the niche is the NULL value of a reference, then `discr_enum_ty` will be