feat(Tactic/FunProp): allow discharging non-prop hypotheses

[grunweg]

As suggested by lecopivo [on zulip](#mathlib4 > Making fun_prop support ContMDiff @ 💬)

This will allow inferring a model with corners, which in turn enables properly supporting ContMDiff and friends in fun_prop.

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Needs a test, and then a prototype to demonstrates this works!

[github-actions]

PR summary 578f407c34

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

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.

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No changes to strong technical debt.

No changes to weak technical debt.