Add/add block comment icon

[poojabhimani12]

What?

Add a new speech bubble icon.

Why?

#59445
https://github.com/WordPress/gutenberg/pull/60622/files#r1739929752

Screenshots or screencast

[github-actions]

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[github-actions]

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[youknowriad]

Assuming the design is validated, this looks good to me.

[jasmussen]

This icon should already be present in the library, "comment":