Respect $XDG_CONFIG_HOME/pdb/.pdbrc path for PDB config discovery

Proposal:

Enabling $XDG_CONFIG_HOME/pdb/.pdbrc would let users keep their $HOMEs organized.

The order of discovery and execution of .pdbrc files would be:

• $XDG_CONFIG_HOME/pdb/.pdbrc
• ~/.pdbrc
• ./.pdbrc

1. The choice of /pdb/ subdirectory under $XDG_CONFIG_HOME is questionable.
2. Additional support of $XDG_CONFIG_DIRS is questionable.

I could provide PR if this feature sounds reasonable.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-133733

首先检查链接的 pull request gh-133733 以及现有的 PDB 配置发现入口点。验证发现和执行现在是否按所述顺序覆盖 $XDG_CONFIG_HOME/pdb/.pdbrc、~/.pdbrc 和 ./.pdbrc；完成的标准是所请求的路径行为已实现，并且所有相关检查均通过。