Improve validate_applicable_state error messages - Medium Priority Updates (#5127)

[shrutipatel31]

Summary:

Improve validate_applicable_state error messages across ax/analysis
to be more user-friendly and descriptive:

• Remove self-referential analysis class names from error messages (e.g., "GenerationStrategyGraph requires...", "PredictableMetricsAnalysis requires...", "BaselineImprovementAnalysis requires...") and replace them with action-oriented phrasing (e.g., "A GenerationStrategy must be provided to visualize...").
• Add parenthetical explanations alongside retained domain class names (OptimizationConfig, OutcomeConstraint, ChoiceParameter) to clarify their meaning for users unfamiliar with Ax internals.
• Reword the base "Requires an Experiment." message to the more descriptive "An Experiment must be provided to compute this analysis."
• Remove backtick formatting around class names in error strings.
• Add purpose/context to error messages (e.g., "...to compute probability of feasibility", "...to evaluate baseline improvement").
• Replace "Objective" jargon with plain "single-objective optimization" language in OutcomeConstraintsAnalysis.
• Update test assertions to match the new message wording.

Audited in https://docs.google.com/document/d/1mxkLvXz0SvdWqO9UrVq5hsFY6MlcwDSk7oVRzdU6kN0/edit?tab=t.0 with the help of an AI Agent

Differential Revision: D97528390

[meta-codesync]

@shrutipatel31 has exported this pull request. If you are a Meta employee, you can view the originating Diff in D97528390.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.41%. Comparing base (c8a547d) to head (86f076e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5127      +/-   ##
==========================================
+ Coverage   96.40%   96.41%   +0.01%     
==========================================
  Files         613      613              
  Lines       68187    68219      +32     
==========================================
+ Hits        65737    65775      +38     
+ Misses       2450     2444       -6     

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