Pre-install the .NET SDK in Windows CI runners

[andrewlock]

Summary of changes

Pre-install the .NET SDKs/runtimes in the Windows VMs

Reason for change

Currently we're explicitly installing the .NET SDK/runtime in the Windows stages. This takes time. Seeing as we pre-build the Windows VMs anyway, we can just pre-install the .NET SDKs there, and set the PATH/DOTNET_32 variables in the VMs.

Implementation details

Updated the VMs to pre-install the .NET SDKs, and remove the tasks that were installing the SDKs in the pipeline.

Note that we still need to install the SDKs in several places:

• When we use the Azure Devops runners - which currently we use for the smoke tests.
• The macOS stages, because they're hosted runners

Test coverage

Ran a full test, and all looks good AFAICT.

Other details

Updated the documentation to include pre-installing the SDKs

[datadog-datadog-prod-us1]

Datadog Report

All test runs ff5c2f5 🔗

✅ 2 Total Test Services: 0 Failed, 2 Passed
❄️ 1 with New Flaky

Test Services

Service Name	Failed	Known Flaky	New Flaky	Passed	Skipped	Total Time	Test Service View
dd-trace-dotnet	0	0	2	576623	9017	67h 55m 12.34s	Link
exploration_tests	0	0	0	22085	3	14m 55.97s	Link

[andrewlock]

Execution-Time Benchmarks Report ⏱️

Execution-time results for samples comparing the following branches/commits:

• This PR (7001)
• master

Execution-time benchmarks measure the whole time it takes to execute a program. And are intended to measure the one-off costs. Cases where the execution time results for the PR are worse than latest master results are shown in red. The following thresholds were used for comparing the execution times:

• Welch test with statistical test for significance of 5%
• Only results indicating a difference greater than 5% and 5 ms are considered.

Note that these results are based on a single point-in-time result for each branch. For full results, see the dashboard.

Graphs show the p99 interval based on the mean and StdDev of the test run, as well as the mean value of the run (shown as a diamond below the graph).

gantt
    title Execution time (ms) FakeDbCommand (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (68ms)  : 66, 70
     .   : milestone, 68,
    master - mean (68ms)  : 66, 70
     .   : milestone, 68,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (1,008ms)  : 989, 1028
     .   : milestone, 1008,
    master - mean (1,007ms)  : 987, 1027
     .   : milestone, 1007,

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gantt
    title Execution time (ms) FakeDbCommand (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (102ms)  : 101, 104
     .   : milestone, 102,
    master - mean (102ms)  : 100, 104
     .   : milestone, 102,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (689ms)  : 668, 710
     .   : milestone, 689,
    master - mean (694ms)  : 676, 712
     .   : milestone, 694,

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gantt
    title Execution time (ms) FakeDbCommand (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (89ms)  : 87, 91
     .   : milestone, 89,
    master - mean (89ms)  : 87, 91
     .   : milestone, 89,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (652ms)  : 629, 675
     .   : milestone, 652,
    master - mean (656ms)  : 633, 679
     .   : milestone, 656,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (189ms)  : 186, 193
     .   : milestone, 189,
    master - mean (190ms)  : 187, 193
     .   : milestone, 190,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (1,112ms)  : 1084, 1140
     .   : milestone, 1112,
    master - mean (1,119ms)  : 1086, 1153
     .   : milestone, 1119,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (268ms)  : 264, 271
     .   : milestone, 268,
    master - mean (268ms)  : 264, 272
     .   : milestone, 268,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (873ms)  : 841, 905
     .   : milestone, 873,
    master - mean (877ms)  : 846, 907
     .   : milestone, 877,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7001) - mean (261ms)  : 257, 265
     .   : milestone, 261,
    master - mean (261ms)  : 258, 264
     .   : milestone, 261,

    section CallTarget+Inlining+NGEN
    This PR (7001) - mean (867ms)  : 829, 904
     .   : milestone, 867,
    master - mean (867ms)  : 845, 889
     .   : milestone, 867,

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[bouwkast]

Awesome thanks!

[NachoEchevarria]

Thanks!