Add `$ifExists` and `$cascade` to `dropTable()` methods

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	✔️
Fix #773

• https://github.com/yiisoft/db-sqlite/pull/319

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.26%. Comparing base (53e81d2) to head (04e0431). Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #880   +/-   ##
=========================================
  Coverage     99.26%   99.26%           
- Complexity     1539     1541    +2     
=========================================
  Files            98       98           
  Lines          3805     3808    +3     
=========================================
+ Hits           3777     3780    +3     
  Misses           28       28           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.