chore(Tactic/GCongr): deprecate Tactic/GCongr/CoreAttrs

[JovanGerb]

This PR moves the @[gcongr] attributes that are in Mathlib.Tactic.GCongr.CoreAttrs to Mathlib.Tactic.GCongr and deprecates the former file.

This follows the same pattern as e.g. to_additive of putting the basic attributes/setup in the root file of the tactic implementation.

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[github-actions]

PR summary 457c164c68

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.Tactic.GCongr	148	147	-1 (-0.68%)

Import changes for all files

Files	Import difference
../mathlib-ci/scripts/pr_summary/import_trans_difference.sh all
There are 7931 files with changed transitive imports taking up over 352456 characters: this is too many to display!
You can run this locally from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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Declarations diff (regex)

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit 457c164).

• +0 new declarations
• −0 removed declarations

No declaration differences.

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No changes to strong technical debt.
No changes to weak technical debt.

Current commit 457c164c68
Reference commit 08c58d241f

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.py 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).