Add Core.declare_const and Core.declare_global

[xal-0]

This change adds the two new builtins that should eventually land, Core.declare_global (JuliaLang/julia#58279) and Core.declare_const (JuliaLang/julia#58187). No other changes should be necessary, but the code that handles the lowered forms of :global, :globaldecl, and :const can eventually be deleted when support for the last version of Julia with those Expr heads is dropped.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.05%. Comparing base (376d172) to head (4bab762).
⚠️ Report is 76 commits behind head on master.

Files with missing lines	Patch %	Lines
src/builtins.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #699      +/-   ##
==========================================
+ Coverage   81.03%   85.05%   +4.02%     
==========================================
  Files          12       12              
  Lines        2636     2730      +94     
==========================================
+ Hits         2136     2322     +186     
+ Misses        500      408      -92     

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