This patch moves the following parsing method to ParserBase:

- DesugarAsyncFunctionBody, renamed to ParseAsyncFunctionBody
- ParseAsyncFunctionExpression, renamed to ParseAsyncFunctionLiteral
- ParseAsyncFunctionDeclaration

It renames the parser implementation methods:

- ParseArrowFunctionFormalParameterList -> DeclareArrowFunctionFormalParameters
- ParseArrowFunctionFormalParameters -> AddArrowFunctionFormalParameters

It also eliminates method ParseAsyncArrowSingleExpressionBody.

R=adamk@chromium.org, marja@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2372733002
Cr-Commit-Position: refs/heads/master@{#39788}