Fix: remove some unicode chars from en/ docs

[evdcush]

Motivation

I am trying to make latexpdf the en/ docs.
Fullwidth chars cause issues for latexpdf build targets, so I replaced them with their normal (half-width) variants.

Modification

• Added some missing papertype indicators in docs
• Replaced some unicode fullwidth chars with their halfwidth variants in docs and python code

Use cases

You used to be able to download the docs as pdf until v3.1.0.
I don't know what broke this, but at least some of the work done in this branch should help narrow down probable causes of the pdf build breakage.

Checklist

1. ✅ Pre-commit or other linting tools are used to fix the potential lint issues.
2. ✅ The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. ✅ If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMPreTrain.
4. ✅ The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.

[evdcush]

How long do PRs typically remain in the pr_stage_test/hold phase?