Merge pull request #4105 from boingoing:DeferParseLambda_3

Fix up the parser to enable the defer parse methods to handle lambda functions. All lambdas are allowed to be deferred, even lambdas with compact parameter lists or function bodies.

Should also allow lambda functions to be redeferred, which is really the main reason to do this work.

One of the related changes is in `Parser::Parse`. I changed this function to skip calling `ParseStmtList` in the case where we are defer parsing a single function. In these cases we know that we are going to parse a function so we don't need to start parsing a set of statements, then one statement, then one expression, then one terminal, etc until we finally start parsing the function via `ParseFncDecl`. Instead we can just jump directly to `ParseFncDecl` after setting up the correct flags. By doing this, we can avoid reparsing the lambda parameter list (because we never assume it will be an ordinary expression list) which saves us the headache of bookkeeping the block and function ids.

One other change of note is in `ScopeInfo::SaveSymbolInfo`. We now need to save symbol info for the `arguments` symbol since a lambda may be deferred in a function and lambdas capture the `arguments` value from their parent. I suppose we could move the `arguments` default binding into a regular special symbol at some point in the future.

…a functions

Merge pull request #4105 from boingoing:DeferParseLambda_3

Fix up the parser to enable the defer parse methods to handle lambda functions. All lambdas are allowed to be deferred, even lambdas with compact parameter lists or function bodies.

Should also allow lambda functions to be redeferred, which is really the main reason to do this work.

One of the related changes is in `Parser::Parse`. I changed this function to skip calling `ParseStmtList` in the case where we are defer parsing a single function. In these cases we know that we are going to parse a function so we don't need to start parsing a set of statements, then one statement, then one expression, then one terminal, etc until we finally start parsing the function via `ParseFncDecl`. Instead we can just jump directly to `ParseFncDecl` after setting up the correct flags. By doing this, we can avoid reparsing the lambda parameter list (because we never assume it will be an ordinary expression list) which saves us the headache of bookkeeping the block and function ids.

One other change of note is in `ScopeInfo::SaveSymbolInfo`. We now need to save symbol info for the `arguments` symbol since a lambda may be deferred in a function and lambdas capture the `arguments` value from their parent. I suppose we could move the `arguments` default binding into a regular special symbol at some point in the future.