Replace old 150-token list with 511-token tokenList.js

Delete src/shared/tokens.js and migrate all consumers to
src/shared/tokenList.js which has 511 tokens (vs ~150) sourced
from CoinGecko with on-chain verified decimals.

- prices.js: getTopTokenPrices now from tokenList
- transactions.js: KNOWN_SYMBOLS now from tokenList (3.4x more
  symbols for spoof detection)
- send.js: KNOWN_SYMBOLS for token dropdown filtering
- approval.js: uses pre-built TOKEN_BY_ADDRESS map instead of
  constructing its own from TOKENS array
- addToken.js: uses getTopTokens(25) for quick-pick buttons
  (only top 25 shown, not all 511)

src/popup/views/send.js

@@ -4,7 +4,7 @@ const { $, showFlash, addressDotHtml, escapeHtml } = require("./helpers");
 const { state, currentAddress } = require("../../shared/state");
 let ctx;
 const { getProvider } = require("../../shared/balances");
-const { KNOWN_SYMBOLS } = require("../../shared/tokens");
+const { KNOWN_SYMBOLS } = require("../../shared/tokenList");
 
 const EXT_ICON =
     `<span style="display:inline-block;width:10px;height:10px;margin-left:4px;vertical-align:middle">` +