RFR: 8261940: Fix references to IOException in BigDecimal javadoc [v2]

[Joe Darcy]

> Noticed by some of  Jon Gibbons's doc linting & checking tooling, this changeset fixes two javadoc issues for BigDecimal's serialization-related methods, improving the serial form page.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2623/files
  - new: https://git.openjdk.java.net/jdk/pull/2623/files/27ff1d78..e3a1659f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2623&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2623&range=00-01

  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2623.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2623/head:pull/2623

PR: https://git.openjdk.java.net/jdk/pull/2623