Remove Apex feature flag & delete CLI code path

[AnanyaJha]

What does this PR do?

This PR removes the Apex setting and the CLI code path for the following functionality:

• SFDX: Get Apex Debug Logs
• SFDX: Execute Anonymous Apex with Currently Selected Text/with Editor Contents
• SFDX: Run Apex Tests, Run Tests Code Lens & Run Tests from Sidebar

apologies in advance, the PR touches lots of files 😅

What issues does this PR fix or reference?

@W-8911035@

[codecov]

Codecov Report

Merging #3148 (16702da) into develop (dee99aa) will increase coverage by 0.01%.
The diff coverage is 75.00%.

@@             Coverage Diff             @@
##           develop    #3148      +/-   ##
===========================================
+ Coverage    76.01%   76.03%   +0.01%     
===========================================
  Files          276      276              
  Lines        10548    10409     -139     
  Branches      1241     1219      -22     
===========================================
- Hits          8018     7914     -104     
+ Misses        2183     2156      -27     
+ Partials       347      339       -8     

Impacted Files	Coverage Δ
...rcedx-vscode-apex/src/commands/forceApexExecute.ts	85.93% <ø> (+7.04%)	⬆️
...rcedx-vscode-apex/src/commands/forceApexTestRun.ts	85.71% <ø> (-2.29%)	⬇️
...de-apex/src/commands/forceApexTestRunCodeAction.ts	72.16% <0.00%> (-10.57%)	⬇️
packages/salesforcedx-vscode-apex/src/settings.ts	100.00% <ø> (ø)
...s/salesforcedx-vscode-apex/src/views/testRunner.ts	69.11% <ø> (-0.89%)	⬇️
...rcedx-vscode-core/src/settings/sfdxCoreSettings.ts	45.00% <ø> (+2.14%)	⬆️
...orcedx-vscode-apex/src/commands/forceApexLogGet.ts	54.76% <100.00%> (+10.05%)	⬆️
...rcedx-vscode-apex/src/views/testOutlineProvider.ts	62.50% <100.00%> (-3.44%)	⬇️
... and 1 more

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[brpowell]

@smaddox-sf I think we'll need to remove the information about the setting on the doc site, but not sure about what other parts of the page should be updated now that this is the only way of running apex commands.

[lcampos]

@AnanyaJha the code looks good and the only remaining update needed is to the Japanese doc article for perf enhancements since it's currently written in English.

[ekapner]

A few minor editorial tweaks. I hope I made my changes in both en and ja versions.

[ekapner]

Thanks for implementing the edits