* Function calls that happen in a comptime scope get called at
   compile-time. We do this by putting the parameters in place as
   constant values and then running regular function analysis on the
   body.
 * Added `Scope.Block.dump()` for debugging purposes.
 * Fixed some code to call `identifierTokenString` rather than
   `tokenSlice`, making it work for `@""` syntax.
 * Implemented `Value.copy` for big integers.

Follow-up issues to tackle:
 * Adding compile errors to the callsite instead of the callee Decl.
 * Proper error notes for "called from here".
   - Related: #7555
 * Branch quotas.
 * ZIR support?