Python Language Server takes too much memory

[skandavc18]

Issue Type: Performance Issue

The Python Laguage Server uses 1GB+ memory even when VS Code is idle. Please reduce the memory footprint of this extension.

Extension version: 2018.12.1
VS Code version: Code 1.30.2 (61122f88f0bf01e2ac16bdb9e1bc4571755f5bd8, 2019-01-07T22:54:13.295Z)
OS version: Windows_NT x64 10.0.17763

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz (8 x 1800)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled
Memory (System)	7.82GB (2.52GB free)
Process Argv	C:\Users\skand\OneDrive\Desktop\lexer.py
Screen Reader	no
VM	67%

Process Info

CPU %	Mem MB	   PID	Process
    1	   106	 14884	code main
    0	   155	  1348	   gpu-process
    0	    97	 11968	   shared-process
    0	   197	 16212	   window (parser.py - Visual Studio Code)
    0	   126	 10676	     extensionHost
    0	  1013	 13948	       c:\Users\skand\.vscode\extensions\ms-python.python-2018.12.1\languageServer.0.1.75\Microsoft.Python.LanguageServer.exe
    0	    11	 11100	         console-window-host (Windows internal process)
    0	    77	 16456	   window (Issue Reporter)

[DonJayamanne]

Dup of #3724