tool_getparam: add support for --longopt=value

If the long option name ends with an equals sign (`=`), the argument is
the text following on its right side.

This makes the command line parser accept this common style in addition
to the existing way to accept option arguments more similar to how other
command line tools do.

Example: `curl --user-agent=curl-2000 https://example.com/`

Change a few existing tests to use this syntax: 206, 1333, 1335, 1442

Closes #17789

tests/data/test1333

@@ -31,7 +31,7 @@ http
 HTTP POST zero length, chunked-encoded
 </name>
 <command>
--d "" --header "Transfer-Encoding: chunked" http://%HOSTIP:%HTTPPORT/%TESTNUMBER
+-d "" --header="Transfer-Encoding: chunked" http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 </command>
 </client>
 

tests/data/test1335

@@ -30,7 +30,7 @@ http
 HTTP GET with -O without Content-Disposition, -D stdout
 </name>
 <command option="no-output,no-include">
-http://%HOSTIP:%HTTPPORT/%TESTNUMBER -O -D - --output-dir %LOGDIR
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER -O -D - --output-dir="%LOGDIR"
 </command>
 </client>
 

tests/data/test1442

@@ -19,7 +19,7 @@ file
 Check --write-out with trailing \
 </name>
 <command>
-file://localhost/%FILE_PWD/%LOGDIR/non-existent-file.txt --write-out '\'
+file://localhost/%FILE_PWD/%LOGDIR/non-existent-file.txt --write-out='\'
 </command>
 </client>
 

tests/data/test206

@@ -80,7 +80,7 @@ digest
 HTTP proxy CONNECT auth Digest
 </name>
 <command>
-http://test.remote.haxx.se.%TESTNUMBER:8990/path/%TESTNUMBER0002 --proxy http://%HOSTIP:%HTTPPORT --proxy-user silly:person --proxy-digest --proxytunnel
+http://test.remote.haxx.se.%TESTNUMBER:8990/path/%TESTNUMBER0002 --proxy=http://%HOSTIP:%HTTPPORT --proxy-user=silly:person --proxy-digest --proxytunnel
 </command>
 </client>