Fine tune description for ACTION_GET_CONTENT/ACTION_OPEN

User will confuse if menu title showing "Open" when file selected
However, AP may intent to get the URI of the selected files only,
Refactor "Open" to "Select" is more compatible for all use cases

Test: atest DocumentsUITests
      Manual test with Gmail/TestApp for attachments
Bug: 80112687
Bug: 110022264

Change-Id: I25f68b5436b5387d3c8e0dbfd7aec0269020cfec