FileViewer: ViewMode to track what is currently displayed

[gerhardol]

There is at least one issue discussing this that I cannot find right now...

Proposed changes

• Replace a couple of booleans tracking current information in the file viewer with an enum
• Hide actions in GitHub view pull request form that have no functionality
• Refresh Patch and GitHub file viewer pull requests when changing the syntax highlight

This will also be used for the presentation part of #8471 that adds more internal changes as well as for #7825 when unifying code from FormCommit/RevDiff (FileStatusList will be required too then).
A CommitDiff mode can remove some duplicated code from FormCommit

Screenshots

Note that the title bar is not following the normal style, same for all plugins.

Before

After

Test methodology

Manual

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✒️ I contribute this code under The Developer Certificate of Origin.

[codecov]

Codecov Report

Merging #8496 into master will decrease coverage by 0.15%.
The diff coverage is 59.42%.

@@            Coverage Diff             @@
##           master    #8496      +/-   ##
==========================================
- Coverage   55.29%   55.14%   -0.16%     
==========================================
  Files         894      900       +6     
  Lines       64150    64492     +342     
  Branches    11450    11529      +79     
==========================================
+ Hits        35473    35563      +90     
- Misses      25958    26204     +246     
- Partials     2719     2725       +6     

Flag	Coverage Δ
#production	42.01% <59.42%> (-0.11%)	⬇️
#tests	94.79% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[RussKie]

Are there any screenshots to see what's changing? I've never actually used that form...

[gerhardol]

Are there any screenshots to see what's changing? I've never actually used that form...

There are no visual changes

This affects all file viewers

[mstv]

LGTM!
Reviewers should start with the diff of the Reset function.

[RussKie]

Few comments

[gerhardol]

Are there any screenshots to see what's changing? I've never actually used that form...

I apologize, this does change the GitHub PR, I added screenshots.
Also using FixedDiff in the ViewPatch form as well as FormVerify (recover lost objects) (could not get a lost object there, no screenshots and only manual review).

[gerhardol]

@msftbot merge in 24 hours

[ghost]

Hello @gerhardol!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I won't merge this pull request until after the UTC date Sat, 03 Oct 2020 17:55:03 GMT, which is in 1 day

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".