Replace pandas.DataFrame with PyArrow.Table for nullable int typing (#8733)

* Use PyArrow Table for query result serialization

* Cleanup dev comments

* Additional cleanup

* WIP: tests

* Remove explicit dtype logic from db_engine_specs

* Remove obsolete  column property

* SupersetTable column types

* Port SupersetDataFrame methods to SupersetTable

* Add test for nullable boolean columns

* Support datetime values with timezone offsets

* Black formatting

* Pylint

* More linting/formatting

* Resolve issue with timezones not appearing in results

* Types

* Enable running of tests in tests/db_engine_specs

* Resolve application context errors

* Refactor and add tests for pyodbc.Row conversion

* Appease isort, regardless of isort:skip

* Re-enable RESULTS_BACKEND_USE_MSGPACK default based on benchmarks

* Dataframe typing and nits

* Renames to reduce ambiguity

superset/assets/spec/javascripts/sqllab/ExploreResultsButton_spec.jsx

@@ -55,13 +55,11 @@ describe('ExploreResultsButton', () => {
   const mockColumns = {
     ds: {
       is_date: true,
-      is_dim: false,
       name: 'ds',
       type: 'STRING',
     },
     gender: {
       is_date: false,
-      is_dim: true,
       name: 'gender',
       type: 'STRING',
     },

superset/assets/spec/javascripts/sqllab/fixtures.js

@@ -219,13 +219,11 @@ export const queries = [
       columns: [
         {
           is_date: true,
-          is_dim: false,
           name: 'ds',
           type: 'STRING',
         },
         {
           is_date: false,
-          is_dim: true,
           name: 'gender',
           type: 'STRING',
         },
@@ -233,13 +231,11 @@ export const queries = [
       selected_columns: [
         {
           is_date: true,
-          is_dim: false,
           name: 'ds',
           type: 'STRING',
         },
         {
           is_date: false,
-          is_dim: true,
           name: 'gender',
           type: 'STRING',
         },
@@ -291,37 +287,31 @@ export const queryWithBadColumns = {
     selected_columns: [
       {
         is_date: true,
-        is_dim: false,
         name: 'COUNT(*)',
         type: 'STRING',
       },
       {
         is_date: false,
-        is_dim: true,
         name: 'this_col_is_ok',
         type: 'STRING',
       },
       {
         is_date: false,
-        is_dim: true,
         name: 'a',
         type: 'STRING',
       },
       {
         is_date: false,
-        is_dim: true,
         name: '1',
         type: 'STRING',
       },
       {
         is_date: false,
-        is_dim: true,
         name: '123',
         type: 'STRING',
       },
       {
         is_date: false,
-        is_dim: true,
         name: 'CASE WHEN 1=1 THEN 1 ELSE 0 END',
         type: 'STRING',
       },