Various build options (OptionsStep) fixes

[courajs]

• There was code to format a std.builtin.Version, but it was untested, and actually fell through to the default case, declaring the constant a second time, as an invalid expression.
• Because we're doing custom code formatting here, I added a check that the generated code is still valid zig syntax
• Fix specifying enum values with names that are not valid identifiers (fixes Build options cannot be set to enum values which are not valid identifiers #10013)
• Allow arbitrary slices and arrays of primitives
• Add explicit error messaging when an invalid type/value is passed, rather than just generating some invalid code

[courajs]

Not sure the Azure build failure is related to these changes - the tests were running but the job timed out. Maybe another manifestation of #6467?

[courajs]

Ah, or #10008! No rush

[andrewrk]

Thanks!