transformerMetaWordHighlight fail to highlight overlapping text instances

[artt]

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Describe the bug

When using transformerMetaWordHighlight to highlight words that overlap, Shiki fails.

Example:

```js /xx/
xxx
``` .

Shiki will try to create two spans with class highlighted-word: (xx)x and x(xx) and will result in the following error:

Failed to parse Markdown file "...":
Decorations {"line":0,"character":0,"offset":0} and {"line":0,"character":1,"offset":1} intersect.

Perhaps a way to fix is to allow highlighting words by character position?

On a related note, why the use of /.../ that resembles regex?

Reproduction

https://stackblitz.com/edit/shiki-intersect?file=src%2Fpages%2Findex.astro,astro.config.mjs,src%2Fcomponents%2Ftest.md

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests

[artt]

Perhaps instead of doing this:

shiki/packages/transformers/src/transformers/meta-highlight-word.ts

Line 43 in c55865f

const indexes = findAllSubstringIndexes(code, word)

it would be easier to just use regex to get the match indices?