RFR: 8287834: Add SymbolLookup::or method [v3]

[Maurizio Cimadamore]

> This patch adds a simpler method for composing symbol lookups. It is common for clients to chain multiple symbol lookups together, e.g. to find a symbol in multiple libraries.
> 
> A new instance method, namely `SymbolLookup::or` is added, which first searches a symbol in the first lookup, and, if that fails, proceeds to search the symbol in the provided lookup.
> 
> We have considered alternatives to express this, such as a static factory `SymbolLookup::ofComposite` but settled on this because of the similarity with `Optional::or`.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Tweak javadoc

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13954/files
  - new: https://git.openjdk.org/jdk/pull/13954/files/27e82bb6..76578973

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13954&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13954&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13954.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13954/head:pull/13954

PR: https://git.openjdk.org/jdk/pull/13954