Organize imports enhancement

Currently "Organize imports" will do three things:

• Add missing imports
• Remove all unused imports
• Sort existing imports

And there are serveral requests about feature "Organize imports":

Organize import without sorting:

• https://github.com/redhat-developer/vscode-java/issues/1575#issue-677597353
• https://github.com/redhat-developer/vscode-java/issues/1575#issuecomment-879667855

Organize imports (and other code actions) in multiple files:

• https://github.com/redhat-developer/vscode-java/issues/1107
• https://github.com/redhat-developer/vscode-java/issues/2282
• https://github.com/microsoft/vscode-java-pack/issues/1085

We can find rooms to improve. Although we have configuration java.completion.importOrder, it's not such visible and it's hard to "hardcode" a package list for some users. In this way, we can have serveral points to improve:

• Add "Remove all unused imports" quickfix for related warnings https://github.com/eclipse/eclipse.jdt.ls/pull/2280
  • it just remove all unused imports, will not affect existing valid imports
• Add "Add all missing imports" quickfix for related errors https://github.com/eclipse/eclipse.jdt.ls/pull/2292
  • it just add all missing imports, will not affect(sort) existing valid imports
• Support "Add all missing import" when pasting https://github.com/redhat-developer/vscode-java/pull/2795
  • related API: https://github.com/microsoft/vscode/issues/30066
• Support code actions (and formatting maybe) in folder level

没有指定文件或测试。首先查看已链接的 issue 和 pull request，然后跟踪现有的 Organize imports 流程及其针对单个文件的 code actions；在不回归现有添加、移除和排序行为的情况下支持文件夹级别的 code actions，即视为完成。