Quarto VSCode extension does not recognize the chunk labels correctly for Rmd

Bug description

Quarto VS Code extension seems not to be able to recognize chunk labels correctly. I initially thought it was Positron issue but then was told it is about Quarto extension. For rmarkdown files, the chuck label cannot be correctly recognized in Positron unless they are written in the quarto rather than rmarkdown style. See more details and screenshots here: https://github.com/posit-dev/positron/issues/6977

Steps to reproduce

Create a rmd file as follows:

```{r abc}
"hello"
```


```{r def}
#| label: def

"hello"
```

Actual behavior

The OUTLINE in Positron shows as follows:

Expected behavior

Recognize the chunk labels correctly and shown in Positron OUTLINE pane.

Your environment

Positron Version: 2025.03.0 (user setup) build 116
Code - OSS Version: 1.96.0
Commit: 7f0f93873e8b24c9f393bb3586724f4783c5e72c
Date: 2025-03-01T19:05:24.180Z
Electron: 32.2.6
Chromium: 128.0.6613.186
Node.js: 20.18.1
V8: 12.8.374.38-electron.0
OS: Windows_NT x64 10.0.26100

Start by reproducing the issue with the two Rmd chunks shown in the report, then locate the Quarto VS Code extension's chunk-label recognition and outline handling. Done means both abc and def labels are recognized correctly in Positron's OUTLINE pane.