Update colored icons for mimeTypes (1/N)

1.Refactor root icons to use mimetype icons
If docsui can't identify it, use system default mimetype icon
Allow OEMs to customize vector drawable (drawable/drawable-night)

2.Remove duplicate ic_doc_xxx icons from docsui, load from system

Test: atest DocumentsTests
Test: atest IconUtilsTest.java
Bug: 117956209
Change-Id: I938fa537a397b58faee12a2e38cf81592daf6e8b