Simplify DFG::DesiredIdentifiers and make it possible to turn a UniquedStringImpl...

Simplify DFG::DesiredIdentifiers and make it possible to turn a UniquedStringImpl* into an identifierNumber at any time
https://bugs.webkit.org/show_bug.cgi?id=147218

Reviewed by Sam Weinig.

I want to be able to take a UniquedStringImpl* and turn it into an identifierNumber at
various points in my work on https://bugs.webkit.org/show_bug.cgi?id=146929. Currently,
most Nodes that deal with identifiers use identifierNumbers and you can only create an
identifierNumber in BytecodeGenerator. DFG::ByteCodeParser does sort of have the
ability to create new identifierNumbers when inlining - it takes the inlined code's
identifiers and either gives them new numbers or reuses numbers from the enclosing
code.

This patch takes that basic functionality and puts it in
DFG::DesiredIdentifiers::ensure(). Anyone can call this at any time to turn a
UniquedStringImpl* into an identifierNumber. This data structure is already used by
Plan to properly install any newly created identifier table entries into the CodeBlock.

* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::ByteCodeParser):
(JSC::DFG::ByteCodeParser::noticeArgumentsUse):
(JSC::DFG::ByteCodeParser::linkBlocks):
(JSC::DFG::ByteCodeParser::InlineStackEntry::InlineStackEntry):
(JSC::DFG::ByteCodeParser::buildOperandMapsIfNecessary): Deleted.
* dfg/DFGDesiredIdentifiers.cpp:
(JSC::DFG::DesiredIdentifiers::DesiredIdentifiers):
(JSC::DFG::DesiredIdentifiers::numberOfIdentifiers):
(JSC::DFG::DesiredIdentifiers::ensure):
(JSC::DFG::DesiredIdentifiers::at):
(JSC::DFG::DesiredIdentifiers::addLazily): Deleted.
* dfg/DFGDesiredIdentifiers.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@187214 268f45cc-cd09-0410-ab3c-d52691b4dbfc