text: Title: Refactoring: environment variables
  Body: Refactoring:
  
  ### First step
  
  - [x] In completion search by substring instead of search by lprefix. Solved in #5388.
  - [x] Fix setting variable using `xonsh -DVAR=VAL`. Solved in #5396.
  - [x] Group env variables by xonsh components. First step is in #5501
  
  ### Second step
  
  Xonsh has [many environment variables](https://xon.sh/envvars.html) and part of them are marked as `XONSH_` and the rest not. I suggest to add `XONSH_` prefix to all environment variables that are related to xonsh itself i.e. rename `RAISE_SUBPROC_ERROR` to `XONSH_RAISE_SUBPROC_ERROR` etc. Pros: Clear understanding of `env`. The way to remove xonsh env variables by running `env | grep -v XONSH_ | grep -v XONTRIB_`.
  
  - [ ] We need to implemet backwards compatibility: the state of `RAISE_SUBPROC_ERROR` should update `XONSH_SUBPROC_RAISE_ERROR` values.
  
  After this the steps look like:
  1. Add "Deprecated" to `RAISE_SUBPROC_ERROR` doc text.
  2. Create `XONSH_SUBPROC_RAISE_ERROR`.
  3. Enable sync values between these two i.e. if I set `RAISE_SUBPROC_ERROR=1` I expect to have `XONSH_SUBPROC_RAISE_ERROR=1` as well and vice versa.
  
  
  ## For community
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