Parser: fix unexpected diagnostics in debug builds, improve error messages

[auduchinok]

Fixes parser diagnostics in property tests in debug builds. It also improves the error messages.

The diagnostics were added in syntax tree tests for properties, making it more difficult to work on the parser:

(6,0)-(6,1) parse error Incomplete structured construct at or before this point. (no 'in' context found: [[NONTERM_classMemberSpfnGetSetElements];
 [NONTERM_classMemberSpfnGetSetElements; NONTERM_classMemberSpfnGetSetElements];
 [NONTERM_classMemberSpfnGetSetElements; NONTERM_classMemberSpfnGetSetElements;
  NONTERM_classMemberSpfnGetSetElements];
 [NONTERM_classMemberSpfnGetSetElements; NONTERM_classMemberSpfnGetSetElements;
  NONTERM_classMemberSpfnGetSetElements];
 [NONTERM_classMemberSpfnGetSet; NONTERM_classMemberSpfnGetSet];
 [NONTERM_autoPropsDefnDecl]; [NONTERM_autoPropsDefnDecl];
 [NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl;
  NONTERM_autoPropsDefnDecl];
 [NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl;
  NONTERM_autoPropsDefnDecl];
 [NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl;
  NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl];
 [NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl;
  NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl];
 [NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl;
  NONTERM_autoPropsDefnDecl; NONTERM_autoPropsDefnDecl]]). Expected identifier, '(', '(*)' or other token.

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

[github-actions]

🔍 Tooling Safety Check — Clean

(scanned-sha)1ad14e36c25f110b38a5685e83d3e09a9bafdf0f(/scanned-sha)

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[auduchinok]

This is ready.