Change signInWithPassword error handling for empty string emails

[lisajian]

Description

Updates error handling for email cases. Reference for how the backend handles email validation: link.

Fixes #3898

Scenarios Tested

• npm test passes
• Verified against JSSDK Auth Demo App. See screenshot.

Sample Commands

N/A

[codecov-commenter]

Codecov Report

Base: 56.26% // Head: 56.27% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (d7e1b69) compared to base (2354100).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5258   +/-   ##
=======================================
  Coverage   56.26%   56.27%           
=======================================
  Files         309      309           
  Lines       20818    20819    +1     
  Branches     4224     4224           
=======================================
+ Hits        11714    11715    +1     
  Misses       8092     8092           
  Partials     1012     1012           

Impacted Files	Coverage Δ
src/emulator/auth/operations.ts	83.40% <100.00%> (+0.01%)	⬆️

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