fix: add helper getPositionAt to fix incorrect loc

[JounQin]

close #292

The following has been resolved!

I don't know if there is a better and cleaner way without source `code` or `lines`.

---

OK, I found maybe we have to use this approach because the loc column of start node could be incorrect as described at #279 (comment), while the start offset is always correct.

[codecov-io]

Codecov Report

Merging #293 (618e5ec) into master (f5d288a) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #293   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines          512       521    +9     
  Branches       100       100           
=========================================
+ Hits           512       521    +9     

Impacted Files	Coverage Δ
.eslintrc.js	100.00% <ø> (ø)
packages/eslint-mdx/src/helpers.ts	100.00% <100.00%> (ø)
packages/eslint-mdx/src/parser.ts	100.00% <100.00%> (ø)

---

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[JounQin]

@wooorm ready for a patch release!

[wooorm]

@JounQin I can’t release, there’s a typescript error when running tsc -b:

Error: @rollup/plugin-typescript TS2569: Type 'IterableIterator<[number, string]>' is not an array type or a string type. Use compiler option '--downlevelIteration' to allow iterating of iterators.
    at error (~/eslint-mdx/node_modules/rollup/dist/shared/rollup.js:5279:30)
    at throwPluginError (~/eslint-mdx/node_modules/rollup/dist/shared/rollup.js:18240:12)
    at Object.error (~/eslint-mdx/node_modules/rollup/dist/shared/rollup.js:18847:24)
    at Object.error (~/eslint-mdx/node_modules/rollup/dist/shared/rollup.js:18409:38)
    at ~/eslint-mdx/node_modules/@rollup/plugin-typescript/dist/index.js:27:21
    at Array.forEach (<anonymous>)
    at emitDiagnostics (~/eslint-mdx/node_modules/@rollup/plugin-typescript/dist/index.js:22:10)
    at Object.transform (~/eslint-mdx/node_modules/@rollup/plugin-typescript/dist/index.js:465:17)
    at ~/eslint-mdx/node_modules/rollup/dist/shared/rollup.js:19049:25 {
  pluginCode: 'TS2569',
  loc: {
    column: 37,
    line: 103,
    file: '~/eslint-mdx/packages/eslint-mdx/src/helpers.ts'
  },
  frame: '\n' +
    "\x1B[7m103\x1B[0m   for (const [index, { length }] of code.split('\\n').entries()) {\n" +
    '\x1B[7m   \x1B[0m \x1B[91m                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~\x1B[0m\n',
  id: '~/eslint-mdx/packages/eslint-mdx/src/helpers.ts',
  hook: 'transform',
  code: 'PLUGIN_ERROR',
  plugin: 'typescript',
  watchFiles: [
    '~/eslint-mdx/packages/eslint-mdx/src/index.ts',
    '~/eslint-mdx/packages/eslint-mdx/src/helpers.ts',
    '~/eslint-mdx/packages/eslint-mdx/src/parser.ts',
    '~/eslint-mdx/packages/eslint-mdx/src/regexp.ts',
    '~/eslint-mdx/packages/eslint-mdx/src/traverse.ts',
    '~/eslint-mdx/packages/eslint-mdx/src/types.ts'
  ]
}

[wooorm]

Released!