Preparing for AST-based synchronization

[kazcw]

Pull Request Description

Further AST integration and API refinement before introducing the new synchronization mechanism.

closes #8609

Important Notes

API changes:

• Renamed Ast.parseExpression / Ast.parse to better reflect their usage:
  • Ast.parse returns a block or a single expression, depending on its input; this is convenient for expressions expected to be single-line.
  • Ast.parseBlock always treats its input as a block; this is suitable for parsing a file.
• astExtended is no longer needed to access span information. Ast.span provides access to the value when appropriate (the project's committed modules have spans; uncommitted changes or other parsed expressions don't).
• SourceRange is now used everywhere in place of ContentRange--the two types had the same definition.

Features:

• Fix CodeEditor viewing.

Implementation improvements:

• Updated widget update handlers ([GUI2] Widget update handlers #8545) implementation to Ast API.
• Integrated imports more thoroughly with new AST APIs.
• More tests.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.