Fix contract folding by adding skipnl/skipempty

Contract name matching needs to skip newlines and empty lines to properly
match the opening brace for folding. Without this, contracts written with
the brace on the same line as the name wouldn't fold properly.

Author: mhluongo

syntax/solidity.vim

@@ -132,8 +132,8 @@ hi def link yulVarDeclaration   Keyword
 hi def link yulAssemblyOp       Keyword
 
 " Contract
-syn match   solContract          /\<\%(contract\|library\|interface\)\>/ nextgroup=solContractName skipwhite
-syn match   solContractName      contained /\<[a-zA-Z_$][0-9a-zA-Z_$]*/ nextgroup=solContractParent,solContractBody skipwhite
+syn match   solContract          /\<\%(contract\|library\|interface\)\>/ nextgroup=solContractName skipwhite skipnl skipempty
+syn match   solContractName      contained /\<[a-zA-Z_$][0-9a-zA-Z_$]*/ nextgroup=solContractParent,solContractBody skipwhite skipnl skipempty
 syn region  solContractParent    contained start='is' end='{' contains=solContractName,solContractNoise,solContractCommas nextgroup=solContractBody skipwhite skipempty
 syn match   solContractNoise     contained 'is' containedin=solContractParent
 syn match   solContractCommas    contained ','