Meta-issue for "why not promoted" functionality

[stereotype441]

This is a meta-issue for tracking progress towards "why not promoted" functionality for the Dart toolchain. It comprises the following arcs of work:

• core flow analysis API to provide non-promotion reasons to front ends (implemented in a42244f)
• full implementation of core algorithm (provide non-promotion reasons in all circumstances): Full implementation of core "why not promoted" algorithm #44898
• explore the possibility of showing the user promotion attempt locations: Explore the possibility of showing the user promotion attempt locations #44899
• establish documentation links for non-promotion reasons: Establish documentation links for non-promotion reasons #44900
• make "why not promoted" information more discoverable in IntelliJ: Make "why not promoted" information more discoverable in IntelliJ #44901
• expose "why not promoted" information in VS Code: Expose Dart's "why not promoted" information in VS Code Dart-Code/Dart-Code#3136
• expose "why not promoted" information in DartPad: Show analysis corrections and "Open Documentation" link dart-pad#1676
• expose "why not promoted" information in Cider: b/179781271
• make "why not promoted" information more discoverable in command-line analyzer: Make "why not promoted" information more discoverable in command-line analyzer #44904
  • make "why not promoted" information more discoverable in dartanalyzer tool Make "why not promoted" information more discoverable in dartanalyzer tool #45546
• expose "why not promoted" information during internal builds: b/179782591
• test.py error tests should support context messages from the CFE: test.py error tests should support context messages from the CFE #44872
• test.py error tests should support context messages from the analyzer: test.py error tests should support context messages from the analyzer #44905
  • Add support to dart analyze for a JSON based output Add support to dart analyze for a JSON based output #45068
• analyzer integration tests to ensure that the data is being sent to clients (both LSP and legacy protocol): Add integration tests to ensure that error context data is being sent to clients (both LSP and legacy protocol) #44907