[Merged by Bors] - feat: add a congruence lemma for orthogonalProjection

[eric-wieser]

While it is still tricky to rewrite with rw, this makes it work with simp.

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[github-actions]

PR summary 06561e8b57

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

+ orthogonalProjection_congr

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.

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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).

[jsm28]

maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by jsm28.

[dupuisf]

bors r+

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

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