Implement SearchCondition to search all elements on screen when scroll to find

[ko1in1u]

This change is 

[eric100lin]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @ko1in1u)

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snippet_uiautomator/android/app/src/main/java/com/google/android/mobly/snippet/uiautomator/UiObject2Snippet.java line 412 at r1 (raw file):

            @Override
            public String toString() {
              return String.format("SearchCondition[selector=%s]", childBySelector);

nit: For simple concatenation like this, directly using '+' might be slightly more readable and performant, consider: return "SearchCondition[selector=" + childBySelector + "]";

Code quote:

String.format("SearchCondition[selector=%s]", childBySelector)