Generalize the f64 support to support other sizes. Also provide interop
support for `float`, `_Float16`, and `__float128`.
Also lay some groundwork for non-standard floating-point types, though
we don't have any syntax to name them yet.
* Rename the type.
* Change lowering to lower FloatLiteralType values as the placeholder
`{}` value we use for literals instead of as an LLVM f64.
* Change eval to convert the type as part of a floating point
conversion, so that lowering can lower converted constants properly.
For now we still represent a value of FloatLiteralType as a
double-precision APFloat. (That will need to change so that we can
losslessly convert literals to f80 / f128 values, and so that we can
convert literals to f32 values without double-rounding.)
Add missing builtins for float compound assignment, for building a
FloatType, and for converting a float literal to FloatType. Switch
`Core.Float` to being a class and add impls for the various
floating-point operators.
---------
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
Geoff Romer
Richard Smith
