add changeset

.changeset/flat-turtles-repeat.md

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+---
+'openzeppelin-solidity': minor
+---
+
+`Arrays`: deprecate `findUpperBound` in favor of the new `lowerBound`.

.changeset/thick-pumpkins-report.md

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+---
+'openzeppelin-solidity': minor
+---
+
+`Arrays`: add new functions `lowerBound`, `upperBound`, lowerBoundMemory`and`upperBoundMemory` for lookups in sorted arrays with potential duplicates.