Add support for breaking into the first line of code in the new debugger

[DonJayamanne]

Fixes #2299

• Title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• [n/a] Unit tests & code coverage are not adversely affected (within reason)
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)
• [n/a] Dependencies are pinned (e.g. "1.2.3", not "^1.2.3")
• [n/a] package-lock.json has been regenerated if dependencies have changed

[ericsnowcurrently]

LGTM

[codecov]

Codecov Report

Merging #2311 into master will decrease coverage by <.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #2311      +/-   ##
==========================================
- Coverage   75.59%   75.59%   -0.01%     
==========================================
  Files         309      309              
  Lines       14336    14339       +3     
  Branches     2539     2540       +1     
==========================================
+ Hits        10838    10840       +2     
- Misses       3488     3489       +1     
  Partials       10       10

Flag	Coverage Δ
#MacOS	73.88% <80%> (-0.01%)	⬇️
#Windows	74.02% <80%> (ø)	⬆️

Impacted Files	Coverage Δ
src/client/debugger/Common/Contracts.ts	100% <100%> (ø)	⬆️
...c/client/debugger/DebugClients/LocalDebugClient.ts	56.3% <100%> (ø)	⬆️
...lient/debugger/configProviders/pythonV2Provider.ts	86.58% <50%> (-0.92%)	⬇️

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