feat: check indentation of doc-strings, basic version

[grunweg]

Basic version of #27897 (which still has some false positives): let's land this before weeding out the other errors.

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• depends on: [Merged by Bors] - feat: separate linter error message for empty doc-strings #27895
• depends on: [Merged by Bors] - chore: surround commutative diagrams in code blocks #27901
• depends on: chore(OrdNode): format code example in code blocks #27933
• a PR for adding clarifying newlines
• some miscellaneous indentation changes

[github-actions]

PR summary 218e764a49

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ checkFormatting

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

---

No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[mathlib4-dependent-issues-bot]

This PR/issue depends on:

• [Merged by Bors] - feat: separate linter error message for empty doc-strings #27895
• [Merged by Bors] - chore: surround commutative diagrams in code blocks #27901
• chore(OrdNode): format code example in code blocks #27933
  By Dependent Issues (🤖). Happy coding!

[mathlib4-merge-conflict-bot]

This pull request has conflicts, please merge master and resolve them.

[mathlib4-merge-conflict-bot]

This pull request has conflicts, please merge master and resolve them.

[mathlib4-merge-conflict-bot]

This pull request has conflicts, please merge master and resolve them.

[mathlib4-merge-conflict-bot]

This pull request has conflicts, please merge master and resolve them.

[grunweg]

Let's close this in favour of #27897, and re-do the doc-string fixes again.