Emmet: Update Tag changes wrong tag pair in invalid HTML

[the-ress]

VS Code version: Code - Insiders 1.34.0-insider (daf7142, 2019-05-06T22:08:08.969Z)
OS version: Windows_NT x64 10.0.17134

Steps to Reproduce:

1. Create a new HTML document
2. Type:

<form>
    <invalid>
    <span></span>
</form>

3. Put cursor into the <span> tag
4. Invoke "Emmet: Update Tag" command
5. Type form

Expected result: <span> gets changed to <form> even though it's a part of an invalid HTML. (Alternatively it could do nothing and show an error.)

Actual result: <div> gets changed to <form> unexpectedly.

Related issue: #39789

System Info

|Item|Value| |---|---| |CPUs|Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz (4 x 2496)| |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
surface_synchronization: enabled_on
video_decode: enabled
webgl: enabled
webgl2: enabled| |Load (avg)|undefined| |Memory (System)|7.87GB (0.87GB free)| |Process Argv|| |Screen Reader|no| |VM|0%|

Extensions: none

[rzhao271]

Merging this issue into #99896