fix(big-number): big number gets cut off on a Dashboard

[stephenLYZ]

SUMMARY

In the big number chart, we currently use computeMaxFontSize to measure the font size, where the incoming width is the actual width of the chart. After testing, it is found that the calculated font size has a certain error, resulting in truncation in the dashboard. So here we decrease 8px of the width to display fonts of different text lengths well.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

	before	after
6 length
7 length
...	...	...
12 length

Since the minimum font size is 10px, if the text length exceeds 12 in extreme cases, it will be truncated. So user need to resize chart at that moment.

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #20488 (97d9fb9) into master (44f0b51) will not change coverage.
The diff coverage is n/a.

❗ Current head 97d9fb9 differs from pull request most recent head 2430321. Consider uploading reports for the commit 2430321 to get more accurate results

@@           Coverage Diff           @@
##           master   #20488   +/-   ##
=======================================
  Coverage   66.75%   66.75%           
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  Files        1740     1740           
  Lines       65172    65172           
  Branches     6900     6900           
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  Hits        43505    43505           
  Misses      19918    19918           
  Partials     1749     1749           

Flag	Coverage Δ
javascript	51.80% <ø> (ø)

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Impacted Files	Coverage Δ
...lugin-chart-echarts/src/BigNumber/BigNumberViz.tsx	0.00% <ø> (ø)

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