Chore: Update tsconfig base target to es2020

[sampaiodiego]

Proposed changes (including videos or screenshots)

The base files are not split into two other files, a "client" and a "server" file. Both extends the new base one. Packages should extend either "client" or "server" ones:

graph TD;
    base[tsconfig.base.json]-->client[tsconfig.base.client.json];
    base-->server[tsconfig.base.server.json];
    server-->s1["@rocket.chat/models"];
    server-->s2["@rocket.chat/ddp-streamer"];
    server-->s3[...];
    client-->c1["@rocket.chat/ui-theming"];
    client-->c2["@rocket.chat/fuselage-ui-kit"];
    client-->c3[...];

Important changes:

• The client config target have been bumped to es2015 (it was es5 before)
• The server config target have been bumped to es2020
• The default value for jsx is react-jsx
• Raised "noUnusedLocals": true to a base config, so had to remove a bunch of imports to React that were not being used

Issue(s)

Steps to test or reproduce

Further comments

[codecov]

Codecov Report

Merging #27552 (4a5d0af) into develop (61689c8) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop   #27552      +/-   ##
===========================================
- Coverage    43.78%   43.65%   -0.14%     
===========================================
  Files          812      812              
  Lines        17176    17176              
  Branches      1902     1902              
===========================================
- Hits          7521     7498      -23     
- Misses        9402     9425      +23     
  Partials       253      253              

Flag	Coverage Δ
e2e	43.65% <ø> (-0.14%)	⬇️

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[ggazzo]

create a client base, sever base and base base :)