[Canvas] Update limits and change some imports

[ThomThomson]

Summary

This PR updates the limits.yml to reflect that Canvas is actually much smaller than it appears. Also did some small changes to the imports which looks like it shaves off .1kb from the page load. This PR also lowers the dashboard plugin's limit to be more inline with the actual size of the Dashboard plugin.

[ThomThomson]

/ci

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 4943b01

Failed CI Steps

• Jest Tests #1
• FTR Configs #3
• FTR Configs #72
• FTR Configs #87

Test Failures

• [job] [logs] Jest Tests #1 / FilePreview pressing escape calls closePreview
• [job] [logs] FTR Configs #72 / Rule execution logic API Detection Engine - Execution logic @ess @serverless @serverlessQA Machine learning type rules "before all" hook for "should create 1 alert from ML rule when record meets anomaly_threshold"

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
canvas	1228	1227	-1

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
canvas	1.1MB	1.1MB	-4.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
canvas	14.1KB	14.0KB	-117.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
canvas	32	31	-1

Total ESLint disabled count

id	before	after	diff
canvas	36	35	-1

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[nreese]

LGTM
code review only