[Backport] Backports perf fixes to static web assets to RTM

[javiercn]

We improved the build performance to bring back some of the performance we lost in 9.0.

Description

During 9.0 the inner build perf regressed compared to 8.0 (some of this slowdown was expected as we were doing significantly more work compared to 8.0).

We received feedback from customers that it is causing slowdowns on larger builds, so we have analyzed the build pipeline for low hanging fruits that we can tackle to bring back some of the lost performance.

Customer Impact

Build times are slower for warm builds than in 8.0, this PR partially removes the perf gap between 8.0 and 9.0 for warm builds, especially on larger builds.

Regression?

• Yes
• No

No in the sense that nothing is broken, but it works slower.

Risk

• High
• Medium
• Low

[Justify the selection above]

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

---

When servicing release/2.1

• Make necessary changes in eng/PatchConfig.props

[dotnet-policy-service]

Thanks for your PR, @javiercn.
To learn about the PR process and branching schedule of this repo, please take a look at the SDK PR Guide.