feat: add truncate-middle-grapheme-cluster string package

[steff456]

Part of #1062

Description

What is the purpose of this pull request?

This pull request:

• Adds @stdlib/string/base/truncate-middle-grapheme-cluster

Related Issues

Does this pull request have any related issues?

This pull request:

• Part of Tracking issue: refactor string packages handling grapheme clusters in terms of "base" packages #1062

Questions

Any questions for reviewers of this pull request?

No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
string/base/truncate-middle-grapheme-cluster	$\color{green}150/150$ $\color{green}+100.00\%$	$\color{green}14/14$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}150/150$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
string/base/truncate-middle-grapheme-cluster	$\color{green}150/150$ $\color{green}+100.00\%$	$\color{green}14/14$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}150/150$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

We should refactor to make seq a mandatory argument: #1118 (comment).

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
string/base/truncate-middle-grapheme-cluster	$\color{green}149/149$ $\color{green}+100.00\%$	$\color{green}13/13$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}149/149$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

Same description change as in other PRs.