DDL: Add index acceleration demo draft pr

[Benjamin2037]

create sysvar TiDBFastDDL (#3)

• Change TiDBFastDDL to Global scope.
• TiDBFastDDL Variable usage
  1, At beginning of doReorgWorkForCreateIndex, use global variable TiDBFastDDL to detemine whether enable lightning backfill process. After set up lightning, then set
  reorgInfo.IsLightningEnabled to true to show the lightning add index is uded for this DDL job.
  2, Later, check reorgInfo.IsLightningEnabled to control the DDL job level lightning's process.
  Complete lightning env initlize procdeure (Improve Documentation: various corrections of the English usage i… #4)

1. Get max open file limition for lightning, default 1024
2. Set light sorted path：
   2.1 If sysVar DataDir is not a start with / data dir path, then set path to /tmp/lightning
   2.2 otherwise set path to DataDir + "lightning"
   Check whether the lightning sorted path is exist and a dir, if yes then keep use it.
   otherwise create new one.
   3, Set the lightning dir quota, default 10G
   Add one unit test
   uniform lightning related errmessage text to lightning_error file. (fix CurrentTimestamp check error for different timezones #5)
   complete memory track module work.
   refacter memmory manager to resource manager for expand to control concurrent
   base available cpu core number.
   Finsih integrate with lightning concurrency process logic.
   Add log for lightning processing.
   refactor some code`
   complete memory track module work. (tools: add .travis.yml #7)
   complete user cancel and exception part logic implement

• complete memory track module work.
• refacter memmory manager to resource manager for expand to control concurrent
  base available cpu core number.

Finsih integrate with lightning concurrency process logic.

• Add log for lightning processing.
  refactor some code`
  restore logic first stage
  adjust metric of ddl process progress value for lightning solution
  refine import cycle
  set up disk quota
  refine code and add some ut and ft.
  Add config paramemter TiDBlightningSortPath for setting sort parth for add index.
  fix mem reclaim problems
  Add log infromation
  combine the optimizes:
  1, prundecode
  2, json expression
  Add some log information

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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