feat: allow named parameters in mapping types

Co-authored-by: Hari <webmail.hari@gmail.com>

test: add parser and abi test cases

docs: add example on using named parameters for mappings

- Add changelog

feat: update antlr grammar to allow named parameters in mappings

fix: prevent conflicting mapping parameter names

ref: change order of mapping initializers

test: update expectations and fix build

test: add more tests

fix: use common error & code for conflicting params

fix: issue with accessing nested mapping

test: add conflicting params tests for more nested levels

Update libsolidity/analysis/DeclarationTypeChecker.cpp

Co-authored-by: Nikola Matić <nikola.matic@ethereum.org>

fix: error reported with the same code twice

test: add more tests for 3 level nested mapping

Address review comments

test/libsolidity/syntaxTests/natspec/invalid/return_param_amount_differs2.sol

@@ -13,3 +13,4 @@ contract Thing is IThing {
 
     mapping(uint256=>Value) public override value;
 }
+// ----