Remove Theia Support

[likhithanimma1]

Proposed changes

Removing code that deals with Theia environment as to drop the Theia support with v3

Release Notes

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Changelog:

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Updates to Documentation or Tests (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTOR GUIDANCE wiki
• PR title follows Conventional Commits Guidelines
• PR Description is included
• gif or screenshot is included if visual changes are made
• yarn workspace vscode-extension-for-zowe vscode:prepublish has been executed
• All checks have passed (DCO, Jenkins and Code Coverage)
• I have added unit test and it is passing
• I have added integration test and it is passing
• There is coverage for the code that I have added
• I have tested it manually and there are no regressions found
• I have added necessary documentation (if appropriate)
• Any PR dependencies have been merged and published (if appropriate)

Further comments

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (087a324) 93.27% compared to head (e471eb0) 93.34%.

Files	Patch %	Lines
packages/zowe-explorer/src/shared/actions.ts	76.92%	3 Missing ⚠️
packages/zowe-explorer/src/uss/USSTree.ts	85.71%	2 Missing ⚠️
...ges/zowe-explorer/src/command/MvsCommandHandler.ts	94.11%	1 Missing ⚠️
...ges/zowe-explorer/src/command/TsoCommandHandler.ts	94.11%	1 Missing ⚠️
...es/zowe-explorer/src/command/UnixCommandHandler.ts	94.11%	1 Missing ⚠️
packages/zowe-explorer/src/dataset/DatasetTree.ts	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #2706      +/-   ##
==========================================
+ Coverage   93.27%   93.34%   +0.06%     
==========================================
  Files         109      109              
  Lines       10294    10203      -91     
  Branches     2223     2095     -128     
==========================================
- Hits         9602     9524      -78     
+ Misses        691      678      -13     
  Partials        1        1              

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[JillieBeanSim]

when doing a search on the repo for isTheia in this branch a lot shows in the results window, we will want to have all of this removed for this story or can split the story across packages if gets too big

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
0.5% Duplication on New Code

See analysis details on SonarCloud

[zFernand0]

LGTM! 😋

Theia seems to be handling quickpicks kind of ok.
and I confirmed that everything ISTHEIA related was removed from the VSIX that I used to test in Theia 😋

[JillieBeanSim]

This looks good, thanks @likhithanimma1 for these updates
I will create a follow up issue for removal of some documentation in READMEs and launches and other items I see but not necessarily code related.

[JillieBeanSim]

follow up story #2726