[query] unify backend rpc

[ehigham]

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[ehigham]

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• [query] Lowering + Optimisation with implict timing context #14731 : 2 dependent PRs (#14732 , #14748 )
• [query] Lift backend state into {Service|Py4J}BackendApi #14698
• [query] Move LoweredTableReaderCoercer into ExecuteContext #14696
• [query] unify backend rpc #14693 👈 (View in Graphite)
• [query] Remove persistedIr from Backend interface #14692
• [query] Remove lookupOrCompileCachedFunction from Backend interface #14691
• [query] Remove BlockMatrix persist from Backend interface #14690
• [query] Expose references via ExecuteContext #14686
• [query] Unify CloudCredentials and Simplify BatchClient #14684 : 1 other dependent PR (#14747 )
• [query] Use sourcecode.Enclosing to handle timed blocks implicitly #14683
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[ehigham]

this is still used to compute blockmatrix sparsity. All others were just used in tests to test that irs parse (which is done by the _type methods)
I wonder if we can move sparsity into the block matrix type and then this too can be removed?

[ehigham]

Previously this command didn't add the reference to the backend state (See BackendServer and ServiceBackendAPI). It seemed to me that it should. Thoughts?