Vfx/fix/1340654 multiline tooltip output properties

[julienamsellem]

Purpose of this PR

https://fogbugz.unity3d.com/f/cases/1340654/

When a tooltip in a subgraph output property spans on multiple lines text cannot be selected properly

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Testing status

Only tested the scenario described in the fogbugz

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Comments to reviewers

Notes for the reviewers you have assigned.

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
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VFX
/.yamato%252Fall-vfx.yml%2523PR_VFX_2021.2

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[VitaVFX]

Looking good! Tested:
VFX Graph, Subgraph, Subgraph Block, Subgraph block operator
Selecting text, selecting text using shortcuts, copy-paste selected text, insert some text, delete text. 🟢

[iTris666]

lgtm