Fix Token Migration silent failure.

[brandonpage]

Migration always uses the Web Server regardless of the user's preferred login flow because LoginViewModel.generateMigrationAuthorizationPath hard-codes useWebServerAuthentication = true by design. The OAuth callback therefore always carries an authorization code rather than a token fragment so we should exchange it for tokens unconditionally.

[wmathurin]

I think that iOS supports both but I only wrote tests that migrates from using user agent to using web server flow (not the other way around).

Given that user agent is going away and that apps are planning to move to using web server flow before using the new migration APIs, I'm fine with only doing web server flow for refresh token migration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.08%. Comparing base (8d3f50e) to head (4104691).
⚠️ Report is 9 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##                dev    #2892   +/-   ##
=========================================
  Coverage     55.07%   55.08%           
- Complexity     2502     2508    +6     
=========================================
  Files           226      226           
  Lines         17781    17774    -7     
  Branches       2328     2327    -1     
=========================================
- Hits           9793     9790    -3     
+ Misses         6981     6980    -1     
+ Partials       1007     1004    -3     

Components	Coverage Δ
Analytics	48.71% <ø> (ø)
SalesforceSDK	41.73% <100.00%> (-0.01%)	⬇️
Hybrid	59.30% <ø> (ø)
SmartStore	78.22% <ø> (ø)
MobileSync	82.12% <ø> (ø)
React	51.50% <ø> (ø)

Files with missing lines	Coverage Δ
...salesforce/androidsdk/ui/TokenMigrationActivity.kt	83.47% <100.00%> (-0.95%)	⬇️

... and 6 files with indirect coverage changes

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[JohnsonEricAtSalesforce]

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