[GlobalISel][DebugInfo] Propagate debug location for localized constants

After IRTranslator pass, constants are deduplicated and translated into instructions at entry block, having debug locations lost.
Localization of constants may cause emission of extra zero lines in debug_line section, like here https://godbolt.org/z/ecvsxxfKn. In this example, constant gets placed as
a first instruction in entry block, and despite it has no debug location, AsmPrinter emits zero line for it.

If a localized constant has the only user, we can assume that it has the same debug location as its user, since they are placed consequently.

Differential Revision: https://reviews.llvm.org/D128192