stop searching on unresolved build config of associated build files

[Techatrix]

This also reverts the change to the iteration order of #1738

#1629 should be reopened because the issue is in the logic that identifier if a file is associated with a build file. These lines have been added in #863 which caused incorrect associations between file: https://github.com/zigtools/zls/blob/3187c3dce32642daffd3377f08939d56e202cedb/src/DocumentStore.zig#L1224-L1226

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (3187c3d) 75.72% compared to head (3902ad5) 75.75%.

Files	Patch %	Lines
src/DocumentStore.zig	33.33%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1744      +/-   ##
==========================================
+ Coverage   75.72%   75.75%   +0.03%     
==========================================
  Files          35       35              
  Lines       10212    10201      -11     
==========================================
- Hits         7733     7728       -5     
+ Misses       2479     2473       -6     

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