- Add a `simple_legalize()` function that invokes a predetermined set of
legalizations, without depending on the details of the current
backend design. This will be used by the new backend pipeline.
- Separate out `has_side_effect()` from the DCE pass. This will be used
by the new backends' lowering code.
- Add documentation for the `Arm64Call` relocation type.
This commit changes 128-bit constant parsing in two ways:
- it adds the ability to use underscores to separate digits when writing a 128-bit constant in hexadecimal; e.g. `0x00010203...` can now be written as `0x0001_0203_...`
- it adds a new mechanism for parsing 128-bit constants using integer/float/boolean literals; e.g. `vconst.i32x4 [1 2 3 4]`. Note that currently the controlling type of the instruction dictates how many literals to parse inside the brackets.
