Propagate `const` declarations into sparse subdomains' `definedConst` property

[bradcray]

Currently, the internal Chapel implementation of domains has a definedConst field that can be used to determine whether the domain was declared as const or var. However, as noted in https://github.com/chapel-lang/chapel/pull/25243, this does not seem to be set up for sparse subdomains. This has the downside of disabling the domain localization optimization as noted in https://github.com/chapel-lang/chapel/pull/25243 and also means that we can't have the setLocalSubdomain() routine issue an error if the user tries to call it on a const domain (as, I realized today, my test test/distributions/sparseBlock/targLocsLocBlocks.chpl accidentally does).