File execution permissions throughout the codebase is inconsistent

Environment

Unrelated to the operations of the viewer itself

Description

PR with permission changes: https://github.com/secondlife/viewer/pull/5226

Some amount of source files, text files, and other non-executable file type files in the codebase have their permissions set to have execute rights. This is typically undesirable and non-standard, as only scripts such as .sh files and .py files with a script shebang at the start should have execute permissions.
There is also some scripts that should have execution permissions but don't (some .sh scripts and some .py files with a script shebang).

Reproduction steps

Command to find files that shouldn't have execution permissions but do-

git ls-files --format '%(objectmode) %(path)' \
| grep -v '^100644' \
| grep -v '\.sh$' \
| cut -d' ' -f2- \
| while read -r f; do
    head -n1 "$f" 2>/dev/null | grep -q '^#!' || echo "$f"
  done

Command to find files that should have execution permissions that don't (this could take a little while)-

git ls-files --format '%(objectmode) %(path)' \
| grep -v '^100755' \
| cut -d' ' -f2- \
| while IFS= read -r f; do
    case "$f" in
      *.sh) echo "$f"; continue;;
    esac
    head -n1 "$f" 2>/dev/null | grep -q '^#!' && echo "$f"
  done

Start with the two git ls-files permission checks in the issue body and review the changes in merged PR #5226. Verify that non-executable files without a shebang no longer have execute permissions, while .sh files and shebang scripts do; the issue is already addressed by that merged pull request.