Quickcheck falsifying example dump falls over for enums

[mikex-oss]

Describe the bug
If the input argument is an enum, then when the falsifying example is reported, it segfaults on ValueToInterpValue

[ RUN QUICKCHECK        ] blue_is_always_favorite count: 1000
*** SIGSEGV (@0x8), ... received by PID 929 (TID 929) on cpu 29; stack trace: ***
PC: @     0x5570f910052d  (unknown)  xls::dslx::ValueToInterpValue()
    @     0x5570fc25f021       1888  FailureSignalHandler()
    @     0x7fc603949e80  (unknown)  (unknown)
    @     0x5570f910052d        368  xls::dslx::ValueToInterpValue()
    @     0x5570f8fbd40b       2096  xls::dslx::AbstractTestRunner::ParseAndTest()
    @     0x5570f8f85cd9       1232  main
    @     0x7fc6037da3d4        192  __libc_start_main
    @     0x5570f8f8402a  (unknown)  _start
E1113 19:29:42.758104     929 process_state.cc:806] RAW: Raising signal 11 with default behavior

To Reproduce
Steps to reproduce the behavior:

enum Color : u2 {
    White = u2:0,
    Red = u2:1,
    Green = u2:2,
    Blue = u2:3,
}

fn favorite_color(color: Color) -> Color { Color::Blue }

#[quickcheck]
fn blue_is_always_favorite(color: Color) -> bool { favorite_color(color) == Color::White }

Expected behavior
The quickcheck should properly report the falsifying sample when found.

As a workaround, you can use u2 as the input type for the quickcheck arg, and then cast to the enum, i.e.

enum Color : u2 {
    White = u2:0,
    Red = u2:1,
    Green = u2:2,
    Blue = u2:3,
}

fn favorite_color(color: Color) -> Color { Color::Blue }

#[quickcheck]
fn blue_is_always_favorite(color: u2) -> bool { favorite_color(color as Color) == Color::White }

will properly report:

FailureError: The program being interpreted failed! Found falsifying example after 1 tests: [u2:2]