only generate a single source.fixAll code action

[Techatrix]

ZLS generates multiple source.fixAll code actions for each fixup it applies. While this has some advantages, It also causes some issues with certain editors:

• Sublime Text LSP is unsure how to apply multiple code actions at the same time (autofix removes extra line sometimes on pointless discard #2076) (there may be other editors that have the same issue)
• NeoVim's vim.lsp.buf.code_action function will show a popup when trying to apply multiple code actions

A single code action that applies all fixups should resolve these issues.