[Chapel Merge] Replace "initializer" in user's guide variables en

Branch: refs/heads/master
Revision: 3b8c1ba
Author: lydia-duncan
Log Message:

Merge pull request #17357 from lydia-duncan/minorUsersGuideFix

Replace "initializer" in user's guide variables entry with "initial value" where appropriate
[reviewed by @bradcray]

I happened to stumble across this when looking at another thing. I think this
user's guide entry was written before initializers were a key part of the
language. Regardless, "initializer" now means a particular type of method on a
record or class, so instead use "initial value" when talking about that portion
of a variable declaration.

Modified Files:
M doc/rst/users-guide/base/vars.rst

Compare: https://github.com/chapel-lang/chapel/compare/506cbfda5775...3b8c1bad93c9