Support casts in comptime constants

[michaeljklein]

Problem

Attempting to use a cast in an a comptime global:

global SOME_CONSTANT: u64 = 7;
global OTHER_CONSTANT: u64 = 1 << SOME_CONSTANT as u8;

Fails with: Expression invalid in an array-length context

Happy Case

OTHER_CONSTANT is equivalent to 1 << 7u8

Project Impact

Nice-to-have

Impact Context

No response

Workaround

None

Workaround Description

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

Yes

Support Needs

No response