spell checker:
- find the "closest" symbol for the minimum levenshtein distance
- do not report private symbols from import
- remove spurious error messages on private symbols found by the spell checker
- allow ambiguous symbols to be reported
Merge pull request #4143 from rainers/issue13736

Fix 13736 - Spellchecker should prefer symbols from inner scopes
fix Issue 13757 - [CTFE] extern(C) alias declaration does not work in CTFE
fix Issue 13756 - [AA] Allow ref const index on foreach AA iteration
Merge pull request #4152 from 9rnsr/fix13756

Issue 13756 - [AA] Allow ref const index on foreach AA iteration
Merge pull request #4153 from 9rnsr/fix13757

Issue 13757 - [CTFE] extern(C) alias declaration does not work in CTFE
fix Issue 13701 - Associative array values ignore immutability