Make assets:install smarter with symlinks
feature #11312 Make assets:install smarter with symlinks (Roy Van Ginneken)

This PR was squashed before being merged into the 2.6-dev branch (closes #11312).

Discussion
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Make assets:install smarter with symlinks

| Q             | A
| ------------- | ---
| Bug fix?   | no
| New feature?      | yes
| BC breaks?      | no
| Deprecations?      | no
| Tests pass?      | -
| Fixed tickets     | #11297
| License     | MIT
| Doc PR | -

Commits
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6537333 Make assets:install smarter with symlinks