Use LinkedHashSet for deterministic iterations

Test `everySearchTypeGeneratesOneESQuery` depends on method `run` in `ElasticsearchBackendGeneratedRequestTestBase.java` and assert the results with the functionalities of `resourceFile`. The method `run` depends on the iteration order of the `HashSet`. However, `HashSet` does not guarantee any specific order of entries. Tests can fail if the iteration order changes.
## Expected Behavior
Tests should always pass if no changes made to source code

## Current Behavior
Tests may fail or pass with no changes made to the source code.

## Possible Solution
Changing HashSet to LinkedHashSet that make the iteration order deterministic