Update READMEs

[hsubox76]

Since READMEs show up on the npm website, we should make sure they are updated and consistent. Some example import patterns were inconsistent (e.g. import firebase from 'firebase/app' vs import * as firebase from 'firebase/app').

• Removed installation and usage instructions from package READMEs since they are not intended to be installed independently, and have a link to the main Firebase package, which has correct instructions.
• Removed installation instructions from internal packages (util, component, etc.)
• Update all import examples toimport * as firebase pattern.
• Add a note to all-in-one import instructions to look at section below for importing individual packages.

Fixes #3514

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Binary Size Report

Affected SDKs

• @firebase/analytics

  Type	Base (2fa0353)	Head (9578da5)	Diff
  esm2017	9.66 kB	9.89 kB	+229 B (+2.4%)
  main	10.9 kB	11.1 kB	+225 B (+2.1%)
  module	10.6 kB	10.8 kB	+234 B (+2.2%)

• @firebase/database

  Type	Base (2fa0353)	Head (9578da5)	Diff
  browser	269 kB	269 kB	+1 B (+0.0%)
  esm2017	236 kB	236 kB	+1 B (+0.0%)
  main	270 kB	270 kB	+1 B (+0.0%)
  module	268 kB	268 kB	+1 B (+0.0%)

• @firebase/firestore

  Type	Base (2fa0353)	Head (9578da5)	Diff
  browser	247 kB	249 kB	+2.13 kB (+0.9%)
  esm2017	193 kB	195 kB	+1.82 kB (+0.9%)
  main	472 kB	474 kB	+2.41 kB (+0.5%)
  module	244 kB	246 kB	+2.09 kB (+0.9%)
  react-native	193 kB	195 kB	+1.81 kB (+0.9%)

• @firebase/firestore/exp

  Type	Base (2fa0353)	Head (9578da5)	Diff
  browser	187 kB	189 kB	+1.99 kB (+1.1%)
  main	464 kB	467 kB	+2.36 kB (+0.5%)
  module	187 kB	189 kB	+1.99 kB (+1.1%)
  react-native	187 kB	189 kB	+1.97 kB (+1.1%)

• @firebase/firestore/lite

  Type	Base (2fa0353)	Head (9578da5)	Diff
  browser	67.9 kB	64.5 kB	-3.32 kB (-4.9%)
  main	144 kB	141 kB	-2.41 kB (-1.7%)
  module	67.9 kB	64.5 kB	-3.32 kB (-4.9%)
  react-native	67.9 kB	64.6 kB	-3.27 kB (-4.8%)

• @firebase/firestore/memory

  Type	Base (2fa0353)	Head (9578da5)	Diff
  browser	185 kB	187 kB	+1.42 kB (+0.8%)
  esm2017	145 kB	146 kB	+1.33 kB (+0.9%)
  main	347 kB	348 kB	+1.35 kB (+0.4%)
  module	183 kB	185 kB	+1.42 kB (+0.8%)
  react-native	145 kB	146 kB	+1.32 kB (+0.9%)

• firebase

  Type	Base (2fa0353)	Head (9578da5)	Diff
  firebase-analytics.js	28.0 kB	28.3 kB	+318 B (+1.1%)
  firebase-database.js	187 kB	187 kB	+1 B (+0.0%)
  firebase-firestore.js	286 kB	288 kB	+2.01 kB (+0.7%)
  firebase-firestore.memory.js	226 kB	227 kB	+1.34 kB (+0.6%)
  firebase.js	819 kB	821 kB	+2.21 kB (+0.3%)

Test Logs

• Base (2fa0353d): https://github.com/firebase/firebase-js-sdk/actions/runs/195338703
• Head (9578da5a): https://github.com/firebase/firebase-js-sdk/actions/runs/203129378

[Feiyang1]

I think it's okay to keep this section for internal packages in order to provide instruction for Googlers. We have clearly stated that this package is intended to be only used by the Firebase team, so I don't think there is any confusion.

[hsubox76]

I restored Usage but kept Installation removed because I don't think any internal user would (or should) npm install it?

[Feiyang1]

restore the usage?

[hsubox76]

Restored.