PR: Add new icons for replace next, all and selection buttons

[conradolandia]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)
• Included a screenshot or animation (if affecting the UI, see Licecap)

• Removed the old generic icon references in spyder/utils/icon_manager.py.
• Added files:
  • spyder/images/dark/replace_all.svg
  • spyder/images/dark/replace_next.svg
  • spyder/images/dark/replace_selection.svg
  • spyder/images/light/replace_all.svg
  • spyder/images/light/replace_next.svg
  • spyder/images/light/replace_selection.svg

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct:

conradolandia

[ccordoba12]

Great work @conradolandia! I really like this new set of icons.

I also tested your PR locally and it's working as expected.